US 7,177,175 B2Grant
Low power programming technique for a floating body memory transistor, memory cell, and memory array
Issue Date:2007-02-13
•24 Claims
•11 Drawing Sheets
Abstract
There are many inventions described and illustrated herein. In one aspect, the present invention is directed to a memory cell, architecture, and/or array and/or technique of writing or programming data into the memory cell (for example, a technique to write or program a logic low or State “0” in a memory cell employing an electrically floating body transistor. In this regard, the present invention programs a logic low or State “0” in the memory cell while the electrically floating body transistor is in the “OFF” state or substantially “OFF” state (for example, when the device has no (or practically no) channel and/or channel current between the source and drain). In this way, the memory cell may be programmed whereby there is little to no current/power consumption by the electrically floating body transistor and/or from memory array having a plurality of electrically floating body transistors.
Metadata
Assignee
- Innovative Silicon S.A.
Inventors
- Pierre Fazan
- Serguei Okhonin
Application Information
Application Number:US 11/334,338
Filing Date:2006-01-17
Priority Date:2003-09-24
Art Unit:2827
Classifications
IPC:
G11C11/24H01L27/01
Patent Drawings (11 sheets)
Description
Cross-Reference to Related Applications
[0001] This application is a divisional of application Ser. No. 10/941,692, filed Sep. 15, 2004 (still pending), the contents of which are incorporated by reference herein in their entirety. This application claims priority to U.S. Provisional Application Ser. No. 60/505,679, entitled “Low Power Programming Technique for a One Transistor SOI Memory Device”, filed Sep. 24, 2003, the contents of which are also incorporated by reference herein in their entirety.
Background
[0002] This invention relates to a semiconductor memory cell, array, architecture and device, and techniques for controlling and/or operating such cell and device; and more particularly, in one aspect, to a semiconductor dynamic random access memory (“DRAM”) cell, array, architecture and/or device wherein the memory cell includes an electrically floating body in which an electrical charge is stored.
[0003] There is a continuing trend to employ and/or fabricate advanced integrated circuits using techniques, materials and devices that improve performance, reduce leakage current and enhance overall scaling. Silicon-on-Insulator (SOI) is a material in which such devices may be fabricated on or in (hereinafter collectively “on”). Such devices are known as SOI devices and include, for example, partially depleted (PD), fully depleted (FD) devices, multiple gate devices (for example, double or triple gate), and Fin-FET. SOI devices have demonstrated improved performance (for example, speed), reduced leakage current characteristics and considerable enhancement in scaling.
[0004] One type of dynamic random access memory cell is based on, among other things, a floating body effect of SOI transistors. (See, for example, U.S. patent application Ser. No. 10/450,238, Fazan et al., filed Jun. 10, 2003 and entitled “Semiconductor Device”, hereinafter “Semiconductor Memory Device Patent Application”). In this regard, the memory cell may consist of a PD or a FD SOI transistor (or transistor formed in bulk material/substrate) on having a channel, which is disposed adjacent to the body and separated therefrom by a gate dielectric. The body region of the transistor is electrically floating in view of the insulation or non-conductive region (for example, in bulk-type material/substrate) disposed beneath the body region. The state of memory cell is determined by the concentration of charge within the body region of the SOI transistor.
[0005] With reference to FIGS. 1A , 1B and 1C, in one embodiment, semiconductor DRAM array 10 includes a plurality of memory cells 12 each consisting of transistor 14 having gate 16, body region 18, which is electrically floating, source region 20 and drain region 22. The body region 18 is disposed between source region 20 and drain region 22. Moreover, body region 18 is disposed on or above region 24, which may be an insulation region (for example, in SOI material/substrate) or non-conductive region (for example, in bulk-type material/substrate). The insulation or non-conductive region may be disposed on substrate 26.
[0006] Data is written into or read from a selected memory cell by applying suitable control signals to a selected word line(s) 28, a selected source line(s) 30 and/or a selected bit line(s) 32. In response, charge carriers are accumulated in or emitted and/or ejected from electrically floating body region 18 wherein the data states are defined by the amount of carriers within electrically floating body region 18. Notably, the entire contents of the Semiconductor Memory Device Patent Application, including, for example, the features, attributes, architectures, configurations, materials, techniques and advantages described and illustrated therein, are incorporated by reference herein.
[0007] In one embodiment, memory cell 12 of DRAM array 10 operates by accumulating in or emitting/ejecting majority carriers (electrons or holes) 34 from body region 18 of, for example, N-channel transistors. (See, FIGS. 2A and 2B ). In this regard, accumulating majority carriers (in this example, “holes”) 34 in body region 18 of memory cells 12 via, for example, impact ionization near source region 20 and/or drain region 22, is representative of a logic high or “1” data state. (See, FIG. 2A ). Emitting or ejecting majority carriers 30 from body region 18 via, for example, forward biasing the source/body junction and/or the drain/body junction, is representative of a logic low or “0”. (See, FIG. 2B ).
[0008] Several techniques may be implemented to read the data stored in (or write the data into) memory cells 12 of DRAM device 10. For example, a current sense amplifier (not illustrated) may be employed to read the data stored in memory cells 12. In this regard, a current sense amplifier may compare the cell current to a reference current, for example, the current of a reference cell (not illustrated). From that comparison, it may be determined whether memory cell 12 contained a logic high (relatively more majority carries 34 contained within body region 18) or logic low data state (relatively less majority carries 28 contained within body region 18).
[0009] Notably, for at least the purposes of this discussion, a logic high or State “1” corresponds to an increased concentration of majority carries in the body region relative to an unprogrammed device and/or a device that is programmed with a logic low or State “0”. In contrast, a logic low or State “0” corresponds to a reduced concentration of majority carries in the body region relative to an unprogrammed device and/or a device that is programmed with a logic high or State “1”.
[0010] With that in mind, a logic high may be written into an electrically floating body transistor of a memory cell using a number of techniques. For example, a logic high may be written by impact ionization or by using a band-to-band tunneling phenomenon (hereinafter “gate induced drain leakage” or “GIDL”). Briefly, for an N-channel type SOI memory cell, a State “1” may be stored in the memory cell by creating excess holes in the electrically floating body of transistor. These holes are believed to be created by a tunneling mechanism that appears in the silicon at the edge of the drain under specific conditions. As such, where a negative voltage is applied on the gate and a positive voltage is applied on the drain, this voltage difference may create a silicon band bending that then leads to a valence band electron tunneling into the conduction band. (See, FIGS. 3A and 3B PRIOR ART). The GIDL effect or mechanism may be a very efficient manner of writing or storing a logic high (State “1”) because it tends not to cause a channel to form in the body and, as such little to no channel current flows between the source and the drain. The GIDL technique of writing or storing a logic high (State “1”) may reduce the current consumption relative to the impact ionization technique.
[0011] The TABLE 1 compares these two programming techniques or mechanisms.
[0012]
| TABLE 1 | ||
|---|---|---|
| Mechanisms used to write State “1” | ||
| Band to band | ||
| Channel impact ionization | tunneling (GIDL) | |
| Power | SOI Device is ON: 10 to | SOI Device is OFF: |
| 100 μA/μm | low power | |
| Scalability | Scalable for a few | More readily scalable |
| generations | ||
[0013] Conventionally, a logic low or State “0” is written into a conventional SOI memory device while the device is in the “ON” State (for example, when the channel exists between the source and the drain). In particular, with reference to FIG. 4 , conventional programming techniques for writing State “0” employ high voltage on the gate (i.e., a high gate voltage (Vg)) and a high voltage on the drain (i.e., a high drain voltage (Vd)) and, as such, the SOI memory device tends to consume and/or dissipate power (for example, approximately 200 μA/μm to approximately 800 μA/μm). Notably, State “1” is written into the SOI memory device via impact ionization.
[0014] While electrically floating body transistors of memory cells (for example, SOI transistors) of the type described above have low leakage current characteristics, such memory cells consume power when programming a logic low (i.e., removing charge carriers from the body of the SOI device). Moreover, given the need for a sufficiently large programming window (i.e., the difference in current level between a logic high and logic low), that consumption may be relatively large. As such, there is a need for high performance SOI memory cells, devices and arrays having improved performance characteristics (for example, speed and/or programming window, programming current consumption), reduced leakage current characteristics and/or considerably enhanced scaling and density capabilities.
Summary of the Invention
[0015] There are many inventions described and illustrated herein. In a first principal aspect, the present invention is a dynamic random access memory cell for storing a first data state and a second data state, the memory cell comprising an electrically floating body transistor having a source region, a drain region, a body region disposed between the source region and the drain region, wherein the body region is electrically floating, and a gate spaced apart from, and capacitively coupled to, the body region. The electrically floating body transistor includes a first data state, which is representative of a first amount of majority carriers in the body region, and a second data state, which is representative of a second amount of majority carriers in the body region, wherein the first amount of majority carriers is less than the second amount of majority carriers.
[0016] The first data state is provided by applying a first voltage to the gate, a second voltage to the drain region, a third voltage to the source region such that, in response to the first, second and third voltages, majority carriers are removed from the body region through source region. In addition, the second voltage is greater than the first voltage and the absolute value of the difference between the first voltage and the third voltage is less than the absolute value of the threshold voltage of the electrically floating body transistor.
[0017] In one embodiment, the electrically floating body transistor is an N-channel type transistor. In another embodiment, the electrically floating body transistor is a P-channel type transistor.
[0018] Notably, the electrically floating body transistor may include a layout, a geometry or electrical characteristics that provides sufficient capacitive coupling between the drain and the floating body such that, in response to the first, second and third voltages, majority carriers are removed from the body region through source region.
[0019] In one embodiment, the absolute value of the difference between the first voltage and the third voltage is substantially less than the absolute value of the threshold voltage of the electrically floating body transistor. Indeed, in one embodiment, the first and third voltages are the same voltage. In another embodiment, the absolute value of the difference between the second voltage and the first voltage is greater than one volt.
[0020] The second data state, which is representative of a second amount of majority carriers in the body region, may be substantially provided by impact ionization. The second data state may also be substantially provided by band-to-band tunneling of majority carriers from the drain region to the body region.
[0021] In another principal aspect, the present invention is a dynamic random access memory cell for storing a first data state and a second data state. The memory cell comprises an electrically floating body transistor having a source region, a drain region, a body region disposed between the source region and the drain region, wherein the body region is electrically floating, and a gate spaced apart from, and capacitively coupled to, the body region. The electrically floating body transistor includes a first data state, which is representative of a first amount of majority carriers in the body region, and a second data state, which is representative of a second amount of majority carriers in the body region, wherein the first amount of majority carriers is less than the second amount of majority carriers.
[0022] The first data state, in this aspect of the invention, is provided by applying a first voltage to the gate, a second voltage to the drain region, a third voltage to the source region such that, in response to the first, second and third voltages, majority carriers are removed from the body region through drain region. Further, the third voltage is greater than the first voltage and the absolute value of the difference between the first voltage and the second voltage is less than the absolute value of the threshold voltage of the electrically floating body transistor.
[0023] In one embodiment, the electrically floating body transistor is an N-channel type transistor. In another embodiment, the electrically floating body transistor is a P-channel type transistor.
[0024] Notably, the electrically floating body transistor may include a layout, a geometry or electrical characteristics that provides sufficient capacitive coupling between the drain and the floating body such that, in response to the first, second and third voltages, majority carriers are removed from the body region through source region.
[0025] The difference between the first voltage and the second voltage may be substantially less than the threshold voltage of the electrically floating body transistor. Indeed, in at least one embodiment, the first and second voltages are the same voltage value. Further, the absolute value of the difference between the third voltage and the first voltage is greater than one volt.
[0026] The second data state, which is representative of a second amount of majority carriers in the body region, may be substantially provided by impact ionization or by band-to-band tunneling of majority carriers from the source region to the body region.
[0027] In another principal aspect, the present invention is a method of controlling a dynamic random access memory cell comprising an electrically floating body transistor having a source region, a drain region, a body region disposed between the source region and the drain region, wherein the body region is electrically floating; and a gate spaced apart from, and capacitively coupled to, the body region. The method comprises applying a first voltage to the gate, applying a second voltage to the drain region, and applying a third voltage to the source region, wherein the second voltage is greater than the first voltage and the difference between the first voltage and the third voltage is less than the threshold voltage of the electrically floating body transistor. In response to the first, second and third voltages, majority carriers are removed from the body region through source region to provide a first data state having a first amount of majority carriers in the body region, wherein the first data state is different than a second data state in that the first amount of majority carriers is less than the amount of majority carriers in the body region when the electrically floating body transistor is in the second data state.
[0028] In one embodiment, the difference between the first voltage and the second voltage is substantially less than the threshold voltage of the electrically floating body transistor. Notably, the first and third voltages may be the same voltage value. In another embodiment, the absolute value of the difference between the first voltage and the second voltage is greater than one volt.
[0029] The second data state of the electrically floating body transistor, which is representative of a second amount of majority carriers in the body region, is substantially provided by impact ionization or by band-to-band tunneling of majority carriers from the source region to the body region.
[0030] Again, there are many inventions described and illustrated herein. This Summary of the Invention is not exhaustive of the scope of the present invention. Moreover, this Summary of the Invention is not intended to be limiting of the invention and should not be interpreted in that manner. While certain embodiments, features, attributes and advantages of the inventions have been described in this Summary of the Invention, it should be understood that many others, as well as different and/or similar embodiments, features, attributes and/or advantages of the present inventions, which are apparent from the description, illustrations and claims, which follow.
Brief Description of the Drawings
[0031] In the course of the detailed description to follow, reference will be made to the attached drawings. These drawings show different aspects of the present invention and, where appropriate, reference numerals illustrating like structures, components, materials and/or elements in different figures are labeled similarly. It is understood that various combinations of the structures, components, materials and/or elements, other than those specifically shown, are contemplated and are within the scope of the present invention.
[0032] FIG. 1A is a schematic representation of a prior art semiconductor DRAM array including a plurality of memory cells comprised of one electrically floating body transistor;
[0033] FIG. 1B is a three dimensional view of an exemplary prior art memory cell comprised of one electrically floating body transistor (PD-SOI NMOS);
[0034] FIG. 1C is a cross-sectional view of the prior art memory cell of FIG. 1B , cross-sectioned along line C—C′;
[0035] FIGS. 2A and 2B are exemplary schematic illustrations of the charge relationship, for a particular memory state, of the floating body, source and drain regions of a prior art memory cell comprised of one electrically floating body transistor (PD-SOI NMOS);
[0036] FIGS. 3A and 3B PRIOR ART illustrate the GIDL mechanism for writing a logic high or State “1” into an electrically floating body transistor (for example, a PD-SOI NMOS);
[0037] FIG. 4 PRIOR ART is a graphical illustration of writing State “1” and State “0” into a one transistor SOI memory cell (for example, an SOI transistor fabricated using 130 nm FD SOI technology) wherein State “1” is written using an impact ionization technique and State “0” is written using high gate voltage (Vg) and high drain voltage (Vd); and
[0038] FIG. 5 is a graphical illustration of the current programming window (ΔI) as a function of gate voltage (Vg), at a high drain voltage (Vd), for N-channel short channel and non-short channel SOI memory transistor; notably, the voltage applied to the source (Vs) is zero or ground);
[0039] FIG. 6 is a graphical illustration of writing State “1” and State “0” into an SOI memory device (for example, an SOI memory transistor fabricated using 130 nm PD technology) wherein State “1” is written using GIDL technique and State “0” is written using a low voltage on the gate (i.e., a low gate voltage (Vg)) and a high drain voltage (Vd); notably, the voltage applied to the source (Vs) is zero or ground);
[0040] FIG. 7A illustrates a memory array including a plurality of memory cells, each including one electrically floating body transistor having a shared drain region (and bit line) and a common word line, which defines a particular row of memory cells, and exemplary writing and/or programming techniques (including exemplary programming voltage values for a logic low or State “0”) according to one embodiment of the present invention;
[0041] FIG. 7B illustrates a memory array including a plurality of memory cells, each having an electrically floating body transistor, configured in a common source line array and having common word lines, which defines a particular row of memory cells, and exemplary writing and/or programming techniques (including exemplary programming voltage values for a logic low or State “0”) according to one embodiment of the present invention;
[0042] FIG. 8 illustrates a memory cell including two electrically floating body transistors that are configured to have a common source region and connected gates, that may be controlled, programmed and/or operated according to one embodiment of the techniques of the present invention; and
[0043] FIGS. 9A and 9B illustrate the two data states of the memory cell having two electrically floating body transistors of, for example, FIG. 8 .
Detailed Description
[0044] At the outset, it should be noted that there are many inventions described herein as well as many aspects and embodiments of those inventions. In a first aspect, the present invention is directed to a memory cell, architecture, and/or array and/or technique of writing or programming data into the memory cell (for example, a technique to write or program a logic low or State “0” in a memory cell empploying an electrically floating body transistor. In this regard, the present invention programs a logic low or State “0” in the memory cell while the electrically floating body transistor is in the “OFF” state or substantially “OFF” state (for example, when the device has no (or practically no) channel and/or channel current between the source and drain). In this way, the memory cell may be programmed whereby there is little to no current/power consumption by the electrically floating body transistor and/or from memory array having a plurality of electrically floating body transistors.
[0045] In one embodiment, the memory cell includes an electrically floating body transistor having a layout, a geometry (for example, the surface area of the drain-body interface relative to the gate-body area/interface) and/or electrical characteristics that provide sufficient capacitive coupling between the drain and the floating body such that when the voltage applied to the drain region (Vd) is increased, while the difference between the voltage applied to the gate is (Vg) and the voltage applied to the source (Vs) is less than the threshold voltage (Vt) of the transistor, majority carriers are removed from the floating body region. A memory cell including such a transistor may be characterized as a short channel (“SC”) memory cell.
[0046] For example, a logic low or State “0” may be written into the memory cell by applying a low gate-source voltage to the transistor comprising the memory cell, for example, at a voltage whereby the transistor remains in the “OFF” state or in a substantially “OFF” state. With reference to FIG. 5 , applying low voltage to the gate such that the difference to the gate-source voltage (Vgs) is small (for example, (1) where there is no channel formation between the source and drain regions and/or (2a) in the context of an N-channel transistor, where the Vgs is less than the threshold voltage of the electrically floating body transistor of the memory cell is in the “OFF” state or essentially in the “OFF” state (for example, when there is little to no channel and/or channel current between the source and drain regions of the transistor) or (2b) in the context of a P-channel transistor, where the absolute value of Vgs is less than the transistor threshold voltage) the electrically floating body transistor of the memory cell is in the “OFF” state or essentially in the “OFF” state (for example, when there is little to no channel and/or channel current between the source and drain regions of the transistor).
[0047] Thus, in those situations where the memory transistor includes the drain-to-body capacitive coupling characteristics of a SC memory cell, writing or programming a State “0” or logic low may be accomplished when the electrically floating body transistor of the memory cell is in the “OFF” state or essentially in the “OFF” state. Notably, the electrically floating body transistor of the memory cell also includes an enhanced efficiency, relative to the programming window, at a low gate-source voltages (Vgs) in the context of N-channel transistors or at low gate-source voltages (Vgs) in the context of P-channel transistors (for example, when the absolute value of the gate-source voltage is less than the absolute value of the threshold voltage of the electrically floating body transistor of the memory cell; and, in this N-channel transistor example, when gate-source voltage (Vgs) is less than 0.25 volts (Vt>Vgs). Indeed, in this example, the SC memory cell includes a greater efficiency, relative to the programming window when the gate-source voltage (Vgs) is 0 volts or about 0 volts
[0048] Notably, where the electrically floating body transistor of the memory cell lacks the drain-to-body capacitive coupling characteristics of a SC device, writing State “0” may require a high gate voltage-source (Vgs) (for example, greater than the transistor threshold voltage).
[0049] With reference to FIG. 6 , the writing, programming and/or control technique, according to the present invention, employs a low gate-source voltage (Vgs) and a high drain voltage (Vd) to write State “0” in the electrically floating body transistor of the memory cell. In one embodiment, State “0” is written and/or programmed into the electrically floating body transistor of the memory cell while the transistor is “OFF”, essentially “OFF” or substantially “OFF” since it consumes essentially no power (i.e., little to no power). (See, dotted area 36 in FIG. 6 ). In this way, the power consumption of the memory cell is considerably less than the consumption observed using other programming techniques.
[0050] Notably, the present invention may be implemented using any technique or operation to write or store a logic high or State “1” in the electrically floating body transistor of the memory cell. For example, impact ionization or GIDL techniques may be employed when writing or storing State “1”. Indeed, any technique, whether now known or later developed may be employed to write or store a logic high or State “1” in the electrically floating body transistor of the memory cell.
[0051] Moreover, the present invention may be implemented using programming techniques whereby the majority carriers are removed from the source and/or drain regions. For example, in one embodiment, all or substantially all of the majority carriers are removed from the source region. In this embodiment, a logic low or State “0” (i.e., majority carriers are removed from the body) is written or programmed into the electrically floating body transistor of the memory cell by applying a low gate-source voltage (Vgs) to the electrically floating body transistor of the memory cell—that is, (1) where there is no channel formation between the source and drain regions of the transistor and/or (2a) where the gate-source voltage (Vgs), in the context of an N-channel transistor, is less than (or substantially less than) the threshold voltage of the transistor or (2b) where the gate-source voltage (Vgs), in the context of an P-channel transistor, is greater than the threshold voltage of the transistor (i.e., the gate-source voltage is less negative than the threshold voltage). In one embodiment, all or substantially all of the majority carriers are removed from the source region.
[0052] Thus, a logic low or State “0” may be programmed into an N-channel electrically floating body transistor of the memory cell by applying a high voltage to the drain region (Vd) (for example, greater than or equal to 0.5 volts, preferably greater than or equal to 1 volt, and more preferably greater than or equal to 1.5 volts) and maintaining or applying a low voltage on the gate (i.e., a low gate voltage (Vg) such that Vgs is less than the threshold voltage of the transistor). (See, for example, transistor 14a1 of memory cell 12a1 in FIG. 7A ). In this regard, the electrically floating body transistor of the memory cell may have sufficient capacitive coupling between its drain and the floating body such that by applying a high drain voltage and a low gate voltage, the majority carriers in the body are removed from the source and/or drain of the device. Again, in this exemplary embodiment, the majority carriers in the body are removed from the source region of the transistor.
[0053] The read and write operations may be performed by controlling the amplitude and timing of the voltages applied to the gate, drain region and source region of electrically floating body transistor 14. For example, with reference to FIG. 7A , memory cell 12a1 may be programmed when word line 28a and bit line 32a are selected, via memory cell selection circuitry 40 and programming circuitry 42, respectively. In this regard, memory cell selection circuitry 40 applies a low voltage on the gate (i.e., a low gate voltage (Vg) such that Vgs is less than the threshold voltage of the transistor, for example, 0 volts). In addition, in one exemplary embodiment, memory cell selection circuitry 40 applies a sufficiently high voltage (1.5 v), in the case of an N-channel transistor, on bit line 32a. In this way, a logic low or State “0” (i.e., majority carriers are removed from the electrically floating body region through the source region) is written or programmed into transistor 14a1 of the memory cell 12a1.
[0054] Notably, where memory cell 12 is one of many or a plurality of memory cells in memory array 10, memory cell selection circuitry 40 may be a conventional word line and bit line decoder or driver. Moreover, pass gates and/or column switch circuitry (not illustrated) may be employed to selectively connect transistor 14a1 to programming circuitry 40 to facilitate and/or implement the programming operation of memory cell 12a1. Indeed, there are many different control/selection techniques (and circuitry therefor) to implement the read and write operations. All such control/selection techniques and circuitry therefor, whether now known or later developed, are intended to fall within the scope of the present invention.
[0055] Briefly, to perform a read operation, sense amplifier 44 (for example, a conventional cross-coupled sense amplifier) is connected to bit lines 32 to detect, determines, sense and/or sample the data state of memory cell 12. In one embodiment, sense amplifier 44 detects the data state of memory cell 12 by comparing the voltages or currents applied to inputs 44a and 44b. The voltage or current applied to input 44a of sense amplifier 44 will depend, to a large extent, on the threshold voltage of the transistor 14 of the selected memory cell 12. The voltage applied to input 44b will depend on the reference voltage that is provided or output by reference circuitry 46.
[0056] In one embodiment, reference circuitry 46 may be a voltage reference or a current source. Where reference circuitry 46 is a current source, the output current of the current source should provide an appropriate voltage or current at input 44b of sense amplifier 44 to permit sense amplifier 44 to detect the data state of memory cell 12. That is, in one embodiment, the amount of current output would be between the amount of current equivalent to a high data state and a low data state of a typical electrically floating body transistor 14 of a typical memory cell 12. In a preferred embodiment, the amount of current is substantially equal to one-half of the sum of the amount of current equivalent to a high data state and a low data state of a typical electrically floating body transistor 14.
[0057] In another embodiment, reference circuitry 46 includes at least two reference memory cells (not illustrated), each including an electrically floating body transistor. In this embodiment, one of the reference memory cells is programmed to a high data state and one of the reference memory cells is programmed to a low data state. The reference circuitry 46, in one embodiment, provides a voltage at input 44b that is substantially equal to one-half of the sum of the two reference memory cells. The memory cell 10 is read by coupling the drain region of the electrically floating body transistor 14 of the selected memory cell 12 to input 44a and the reference voltage generated by reference circuitry 46 to input 44b.
[0058] It may be advantageous to employ the reference memory cells configuration described above in order to track and/or address variations in the memory cell characteristics due to changes in operating conditions (for example, temperature variations and/or power variations).
[0059] Thus, the circuitry employed to read the data state of memory cell 10 (for example, sense amplifier 44 and reference circuitry 46) may sense the data state stored in memory cell 10 using voltage or current sensing techniques. Such circuitry and configurations thereof are well known in the art. Indeed, any circuitry or architecture to sense, sample, detect or determine the data state of memory cell 12, whether now known or later developed, is intended to be within the scope of the present invention.
[0060] In one embodiment, the source regions of the electrically floating body transistors 14 of the memory cells 12 may be coupled to a stable reference voltage (for example, a ground potential or zero volts) generated by a reference voltage generator (not illustrated). In other embodiments, the source regions of the electrically floating body transistors 14 of the memory cells 12 may be coupled to certain control signals having well defined voltage levels and timing characteristics. (See, for example, the embodiment of FIG. 7B )
[0061] Notably, pass gates and/or column switch circuitry (not illustrated) may be employed to selectively connect electrically floating body transistors 14 to sense amplifier 44 to facilitate and/or implement the read and write operations of the data state of memory cell 12.
[0062] In sum, certain advantages of the State “0” programming technique and the electrically floating body transistor of memory cell (for example, the SOI transistor memory cell) of the present invention include: (1) low power consumption, (2) enhanced scalability and (3) a relatively large programming window (for example, as illustrated in FIG. 6 , ΔIs=30 μA/μm).
[0063] Notably, while a significant portion of this description includes details (for example, write/programming and/or read voltages) directed to N-channel transistors, the inventions (and embodiments thereof) described herein are entirely applicable to P-channel transistors, as described above. In such embodiments, majority carriers 34 in body region 18 are electrons and minority carriers are holes and the voltages applied to the gate, source region and drain region may be negative.
[0064] Moreover, the memory arrays may be comprised of N-channel, P-channel and/or both types of transistors. Indeed, the circuitry that is peripheral to the memory array (for example, sense amplifiers or comparators, row and column address decoders, as well as line drivers (all not illustrated herein)) may include P-channel and/or N-channel type transistors, including short channel type transistors. Where P-channel type transistors are employed as memory cells 12 in the memory array(s), suitable write and read voltages (for example, negative voltages) are well known to those skilled in the art in light of this disclosure. Accordingly, for sake of brevity, these discussions will not be repeated.
[0065] There are many inventions described and illustrated herein. While certain embodiments, features, attributes and advantages of the inventions have been described and illustrated, it should be understood that many others, as well as different and/or similar embodiments, features, attributes and advantages of the present inventions, are apparent from the description and illustrations. As such, the embodiments, features, attributes and advantages of the inventions described and illustrated herein are not exhaustive and it should be understood that such other, similar, as well as different, embodiments, features, attributes and advantages of the present inventions are within the scope of the present inventions.
[0066] For example, the electrically floating body transistor, which is programmed to a logic low or State “0” according to the techniques of the present invention, may be employed in any memory cell, architecture, layout, structure and/or configuration. In this regard, such a transistor may be implemented in the memory cell, architecture, layout, structure and/or configuration described and illustrated in the following non-provisional U.S. patent applications:
[0067] (1) application Ser. No. 10/450,238, which was filed by Fazan et al. on Jun. 10, 2003 and entitled “Semiconductor Device”;
[0068] (2) application Ser. No. 10/487,157, which was filed by Fazan et al. on Feb. 18, 2004 and entitled “Semiconductor Device”;
[0069] (3) application Ser. No. 10/829,877, which was filed by Ferrant et al. on Apr. 22, 2004 and entitled “Semiconductor Memory Cell, Array, Architecture and Device, and Method of Operating Same”; and
[0070] (4) application Ser. No. 10/840,009, which was filed by Ferrant et al. on May 6, 2004 and entitled “Semiconductor Memory Device and Method of Operating Same”. The entire contents of these non-provisional U.S. patent applications, including, for example, the inventions, features, attributes, architectures, configurations, materials, techniques and advantages described and illustrated therein, are hereby incorporated by reference herein.
[0071] For example, with reference to FIG. 7B , one some or all of memory cells 12 of adjacent rows 38a and 38b may be programmed to a logic low or State “0” using the techniques of the present invention. In this exemplary embodiment, memory array 10 includes a plurality of memory cells 12, each have an electrically floating body transistor 14. The memory cells 12a–d of row 38a “share” source line 30a with memory cells 12e–h of row 38b. In this embodiment, the voltages applied to the gate and the drain provides a differential that is less than Vt of the transistor (in this exemplary embodiment, Vgd=0 v). As such, no channel forms between the source and drain of transistor 14 of memory cells 12. The writing or programming a logic low of State “0” into selected memory cells 12c, 12d, 12f and 12g of the architecture of this exemplary memory array is accomplished by applying a write logic low voltage to source line 30a relative to the voltage applied to the gates of the transistors of memory cells 12a–d and 12e–h (in this exemplary embodiment, Vs=1.8 v and Vg=0 v), via a common word line. Notably, in this exemplary embodiment, the majority carriers in the body are ejected or removed from the drain region of the selected transistors.
[0072] Moreover, by applying respective inhibit voltages to selected bit lines memory cells 12a, 12b, 12e and 12h (which are associated or connected to selected bit lines 32a–32h) maintain their data states and, as such, their data states are not affected by the programming of logic low or State “0” in memory cells 12c, 12d, 12f and 12g of rows 38a and 38b.
[0073] Notably, the memory cells may be controlled (for example, programmed, inhibited or read) using memory selection circuitry 40, programming circuitry 42, sense amplifier 44 and reference circuitry 46, as described above, as well as using any of the control/operation techniques described and illustrated in the above-referenced four (4) non-provisional U.S. patent applications. For the sake of brevity, those discussions will not be repeated; such control/operation techniques are incorporated herein by reference.
[0074] It should be further noted that while each memory cell 12 in the exemplary embodiments includes one transistor 14, memory cell 12 may include two transistors 14a and 14b, as described and illustrated in application Ser. No. 10/829,877, which was filed by Ferrant et al. on Apr. 22, 2004 and entitled “Semiconductor Memory Cell, Array, Architecture and Device, and Method of Operating Same”. In this regard, with reference to FIG. 8 , two-transistor memory cell 12 includes transistors 14a and 14b which store complementary data states. In one embodiment, transistors 14a and 14b of memory cell 12 include a layout whereby transistors 14a and 14b include (1) common source regions 20a and 20b, respectively, and (2) gates 16a and 16b, respectively, that are connected to the same word line 28.
[0075] With reference to FIGS. 9A and 9B , in operation, two-transistor memory cell 12 includes first transistor 14a that maintains a complementary state relative to second transistor 14b. As such, when programmed, one of the transistors of the memory cell stores a logic low (a binary “0”) and the other transistor of the memory cell stores a logic high (a binary “1”). The transistor 14 that is programmed to a logic low or State “0” may be programmed according to the techniques of the present invention. That is, transistor 14 of memory cell 12 may be programmed to a logic low or State “0” (i.e., majority carriers are removed from the body) by applying a low gate-source voltage (Vgs) to the electrically floating body transistor of the memory cell. In this way, little to no channel is formed between the source and drain regions of the transistor in the transistor 14 that is programmed to a logic low or State “0” (the gate-source voltage (Vgs), in the context of an N-channel transistor, is less than the threshold voltage of the transistor or the gate-source voltage (Vgs), in the context of an P-channel transistor, is greater than the threshold voltage (Vt) of the transistor (i.e., Vgs is less negative than the Vt).
[0076] As mentioned above, any of the architectures, layouts, structures and/or configurations, as well as the programming and reading operations described and illustrated in application Ser. No. 10/829,877, which was filed by Ferrant et al. on Apr. 22, 2004 and entitled “Semiconductor Memory Cell, Array, Architecture and Device, and Method of Operating Same” may be employed in conjunction with the inventions described and illustrated herein. For the sake of brevity, those discussions will not be repeated; rather, they are incorporated by reference herein.
[0077] The electrically floating memory cells, SC transistors and/or memory array(s) may be fabricated using well known techniques and/or materials. Indeed, any fabrication technique and/or material, whether now known or later developed may be employed to fabricate the electrically floating memory cells, SC transistors and/or memory array(s). For example, the present invention may employ silicon (whether bulk-type or SOI, as described above), germanium, silicon/germanium, and gallium arsenide or any other semiconductor material in which transistors may be formed. Indeed, the electrically floating memory cells, SC transistors and/or memory array(s) may employ the techniques described and illustrated in non-provisional patent application entitled “Integrated Circuit Device, and Method of Fabricating Same”, which was filed on Jul. 2, 2004, by Fazan, and assigned Ser. No. 10/884,481 (hereinafter “Integrated Circuit Device Patent Application”). The entire contents of the Integrated Circuit Device Patent Application, including, for example, the inventions, features, attributes, architectures, configurations, materials, techniques and advantages described and illustrated therein, are hereby incorporated by reference herein.
[0078] Indeed, the memory array 10 (including SOI memory transistors) may be integrated with SOI logic transistors, as described and illustrated in the Integrated Circuit Device Patent Application. For example, in one embodiment, an integrated circuit device includes memory section (having, for example, PD or FD SOI memory transistors 14) and logic section having, for example, high performance transistors, such as Fin-FET, multiple gate transistors, and/or non-high performance transistors (for example, single gate transistors that do not possess the performance characteristics of high performance transistors—not illustrated). Again, the entire contents of the Integrated Circuit Device Patent Application, including, for example, the inventions, features, attributes, architectures, configurations, materials, techniques and advantages described and illustrated therein, are hereby incorporated by reference.
[0079] Notably, electrically floating body transistor 14 may be a symmetrical or non-symmetrical device. Where transistor 14 is symmetrical, the source and drain regions are essentially interchangeable. However, where transistor 14 is a non-symmetrical device, the source or drain regions of transistor 14 have different electrical, physical, doping concentration and/or doping profile characteristics. As such, the source or drain regions of a non-symmetrical device are typically not interchangeable. This notwithstanding, the drain region of the electrically floating N-channel transistor of the memory cell (whether the source and drain regions are interchangeable or not) is that region of the transistor that is connected to the bit line/sense amplifier.
[0080] The above embodiments of the present invention are merely exemplary embodiments. They are not intended to be exhaustive or to limit the inventions to the precise forms, techniques, materials and/or configurations disclosed. Many modifications and variations are possible in light of the above teaching. It is to be understood that other embodiments may be utilized and operational changes may be made without departing from the scope of the present invention. As such, the foregoing description of the exemplary embodiments of the invention has been presented for the purposes of illustration and description. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention not be limited solely to this detailed description but be measured by the claims, which follow.
Claims
What is claimed is:
1. A dynamic random access memory cell for storing a first data state and a second data state, the memory cell comprising:
an electrically floating body transistor having:
a source region;
a drain region;
a body region disposed between the source region and the drain region,
wherein the body region is electrically floating; and
a gate spaced apart from, and capacitively coupled to, the body region;
wherein the electrically floating body transistor includes a first data state representative of a first amount of majority carriers in the body region, and a second data state representative of a second amount of majority carriers in the body region, wherein the first amount of majority carriers is less than the second amount of majority carriers;
wherein the first data state is provided by applying a first voltage to the gate, a second voltage to the drain region, a third voltage to the source region such that, in response to the first, second and third voltages, the electrically floating body transistor is off or substantially off; and
wherein the second voltage is greater than the first voltage and the absolute value of the difference between the first voltage and the third voltage is less than the absolute value of the threshold voltage of the electrically floating body transistor.
2. The dynamic random access memory cell of claim 1 wherein the first and third voltages have the same voltage amplitude.
3. The dynamic random access memory cell of claim 1 wherein the electrically floating body transistor is an N-channel type transistor or a P-channel type transistor.
4. The dynamic random access memory cell of claim 1 the electrically floating body transistor includes a layout, a geometry or electrical characteristics that provides sufficient capacitive coupling between the drain and the floating body such that, in response to the first, second and third voltages, majority carriers are removed from the body region through source region.
5. The dynamic random access memory cell of claim 1 wherein the absolute value of the difference between the first voltage and the third voltage is substantially less than the absolute value of the threshold voltage of the electrically floating body transistor.
6. The dynamic random access memory cell of claim 1 wherein the absolute value of the difference between the second voltage and the first voltage is greater than one volt.
7. The dynamic random access memory cell of claim 1 wherein the second data state which is representative of a second amount of majority carriers in the body region is substantially provided by impact ionization.
8. The dynamic random access memory cell of claim 1 wherein the first and third voltages are the same voltage.
9. The dynamic random access memory cell of claim 1 wherein the second data state is substantially provided by (i) band-to-band tunneling of majority carriers from the drain region to the body region, or (ii) band-to-band tunneling of majority carriers from the source region to the body region.
10. A dynamic random access memory cell for storing a first data state and a second data state, the memory cell comprising:
an electrically floating body transistor having:
a source region;
a drain region;
a body region disposed between the source region and the drain region,
wherein the body region is electrically floating; and
a gate spaced apart from, and capacitively coupled to, the body region;
wherein the electrically floating body transistor includes a first data state representative of a first amount of majority carriers in the body region, and a second data state representative of a second amount of majority carriers in the body region, wherein the first amount of majority carriers is less than the second amount of majority carriers; and
wherein the first data state is provided by applying a first voltage to the gate, a second voltage to the drain region, a third voltage to the source region such that, in response to the first, second and third voltages the electrically floating body transistor is off or substantially off.
11. The dynamic random access memory cell of claim 10 wherein the electrically floating body transistor is off when there is no or substantially no channel and/or channel current between the source and drain regions of the electrically floating body transistor.
12. The dynamic random access memory cell of claim 10 wherein the electrically floating body transistor is an N-channel type transistor or a P-channel type transistor.
13. The dynamic random access memory cell of claim 10 the electrically floating body transistor includes a layout, a geometry or electrical characteristics that provides sufficient capacitive coupling between the drain and the floating body such that, in response to the first, second and third voltages, majority carriers are removed from the body region through drain region.
14. The dynamic random access memory cell of claim 10 wherein the absolute value of the difference between the first voltage and the second voltage is substantially less than the absolute value of the threshold voltage of the electrically floating body transistor.
15. The dynamic random access memory cell of claim 10 wherein the absolute value of the difference between the third voltage and the first voltage is greater than one volt.
16. The dynamic random access memory cell of claim 10 wherein the second data state which is representative of a second amount of majority carriers in the body region is substantially provided by impact ionization.
17. The dynamic random access memory cell of claim 10 wherein the first and second voltages have the same amplitude.
18. The dynamic random access memory cell of claim 10 wherein the second data state is substantially provided by (i) band-to-band tunneling of majority carriers from the source region to the body region, or (ii) band-to-band tunneling of majority carriers from the drain region to the body region.
19. A method of controlling a dynamic random access memory cell comprising an electrically floating body transistor having a source region, a drain region, a body region disposed between the source region and the drain region, wherein the body region is electrically floating; and a gate spaced apart from, and capacitively coupled to, the body region, the method comprising:
applying a first voltage to the gate;
applying a second voltage to the drain region;
applying a third voltage to the source region, wherein, in response to the first, second and third voltages, the electrically floating body transistor is off or substantially off; and
wherein, in response to the first, second and third voltages, a substantial amount of the majority carriers are removed from the body region through the source region or the drain region to provide a first data state having a first amount of majority carriers in the body region, wherein the first data state is different than a second data state of the electrically floating body transistor in that the first amount of majority carriers is less than the amount of majority carriers in the body region when the electrically floating body transistor is in the second data state.
20. The method of claim 19 wherein the absolute value of the difference between the first voltage and the second voltage is greater than one volt.
21. The method of claim 19 wherein the difference between the first voltage and the second voltage is substantially less than the threshold voltage of the electrically floating body transistor.
22. The method of claim 19 wherein the second data state which is representative of a second amount of majority carriers in the body region is substantially provided by impact ionization.
23. The method of claim 19 wherein the first and third voltages have the same amplitude.
24. The method of claim 19 wherein the second data state is substantially provided by (i) band-to-band tunneling of majority carriers from the source region to the body region, or (ii) band-to-band tunneling of majority carriers from the drain region to the body region.
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