Information Processing Device Capable of Optically Writing Synapse Strength Matrix

1. Field of the Invention

The present invention relates to an information processing device in which a synapse strength matrix (Tij) representing inter-neuron wiring in neural information processing can be written by rays of light from light-emitting elements formed in the device.

2. Prior Art

FIG. 1 is a diagram showing an integrated circuit in an information processing device simulating a neural circuit network which is shown, for example, on page 625 of "Science", 233, by J. J. Hopfield et al (1986). In the drawing, the reference numeral 1 indicates a unit of neurons each of which includes a resistor 2, a capacitor 3 and an amplifier 4. The reference numeral 5 indicates a Tij indicative of a level of interaction between neurons. The reference numerals 6 and 7 respectively, indicate an input line connected to the neuron 1 and an output line extending therefrom.

The operation of this integrated circuit will now be described. Information carried by an external signal is supplied, as an input to the processing device, to the neuron 1 in the form, for example, of electric current, through the input line 6. The input line 6 crosses the output line 7 of another neuron at the Tij portions 5 before the input line 6 reaches the neuron 1, the current input to the neuron 1 is affected by the output line 7. The Tij portions 5 generally consist of a fixed resistor formed within the information processing device when that device is manufactured. In the neuron 1, the resistor 2 and the capacitor 3 convert the input current value to a voltage value, which is amplified by the amplifier 4, whereby an output of firing (+V) or suppression (-V) is emitted. When the respective outputs of the neurons of the entire network have attained stability, optimum target information is obtained among these output values.

A conventional information processing device being constructed such as described above, neurons, wiring lines and Tij portions have to be previously formed in the device. As a result, the number of neurons that can be integrated in the device is limited. In addition, the value of Tij portions cannot be changed.

The present invention has been made with a view to solving the above problems. It is accordingly an object of the invention to provide an information processing device which is capable of enhancing the degree of integration of neurons and to allow Tij values to be rewritten with ease.

In accordance with an aspect of the invention, there is provided an information processing device comprising a semiconductor integrated circuit section simulating a neuronic function of a neural network; a photoelectric section including a heterogeneous molecular film having a photoelectric function and placed between electrodes; and a light-emitting section, both photoelectric and light-emitting sections being provided on the integrated circuit section; wherein Tij signals from the light-emitting section can be written in the photoelectric section.

In accordance with another aspect of the invention, there is provided an information processing device in which the photoelectric section and the light-emitting section are formed in a multilayer structure on the semiconductor integrated circuit section in which neuronic circuit regions are arranged in matrix.

According to the present invention, Tij portions coupling the neuronic circuit regions to each other comprise a photoelectric heterogeneous molecular film provided on the semiconductor circuit section in which neuronic circuit regions are provided, and electrodes formed on both sides of the molecular film. Coupling strength between the neurons is input by means of light from a matrix-like light-emitting device which comprises electrodes and a light-emitting heterogeneous molecular film placed therebetween. This structure allows the coupling between the neurons to be changed. Further, in accordance with the invention, the photoelectric section and the light-emitting section both comprising electrodes and a heterogeneous molecular film placed therebetween may be built three-dimensionally on the semiconductor integrated circuit section, whereby the number of neurons that can be integrated per unit area can be increased substantially.

Further, in the present invention, the photoelectric section may be built in a multilayer structure on the semiconductor integrated circuit in which the neuronic circuit regions are arranged in matrix, whereby the number of wiring lines for forming the Tij couplings can be reduced, thereby making it possible to increase the number of neurons that can be integrated.

FIG. 1 is a circuit diagram showing a conventional information processing device;

FIGS. 2(a) and 2(b) are diagrams showing a plan view of a Tij matrix wiring pattern in an information processing device in accordance with an embodiment of the present invention and a partial sectional view of the same;

FIGS. 3(a), 3(b) and 3(c) are diagrams showing a plan view of a neuron connecting pattern in an information processing device in accordance with another embodiment of this invention and partial sectional views of the same; and

FIG. 4 is a chart showing a voltage-current characteristic of a molecular film obtained by heterozygous accumulation.

An embodiment of the present invention will now be described with reference to the accompanying drawings.

FIG. 2(a) is a wiring diagram showing the construction of an information processing device in accordance with an embodiment of this invention and FIG. 2(b) is a sectional view taken along the line A--A' of FIG. 2(a). The device shown includes neurons 11, a molecular film 12 having a photoelectric function, input wiring lines 13, output wiring lines 14, synaptic junction sections 16, a silicon substrate 17, an insulating film 18, electrodes 31 for light-emitting elements, a molecular film 32 having a light-emitting function, a transparent electrode 33 for the light-emitting elements, a transparent insulating layer 34, and lead wires 35 for the electrodes 31.

A method of producing the device of this embodiment will be described next.

The neurons 11 which are formed as analog or digital circuits so as to simulate a neuronic operation of a living body are arranged in columns in the silicon substrate 17 using integrated circuit technologies. Then, the input wiring lines 13 are formed on one surface of the integrated circuit by vacuum evaporation of aluminum. The other surface of the integrated circuit (where no input wiring lines 13 are formed) are covered by an insulating film, such as an SiO.sub.2 film 18, thus leveling the surface of the integrated circuit. On this wafer on which the integrated circuit and the wiring lines have been formed, several layers of porphyrin derivative are deposited by the Langmuir-Blodgett method and, then, several layers of flavin derivative are deposited thereon, thereby forming the heterogeneous molecular film 12.

This molecular film 12 has a property of changing a current flowing between the electrodes in accordance with the intensity of light impinging thereto.

Then, the output wiring lines 14 are formed on the molecular film 12 by vacuum evaporation of aluminum, ITO, SnO.sub.2, etc. such that they overlap the Tij portions 16. In this process, the Tij portions 16 should be transparent so as to allow light to be transmitted to the molecular films.

Subsequently, the transparent insulating layer 34 is formed on the molecular film 12 and the output wiring lines 14 by using SiO.sub.2, a high molecular substance, etc., and, on this layer 34, the transparent electrode 33 is formed of such material as ITO, SnO.sub.2 and aluminum.

Then, an amine-type material, such as TPD IN, N'-diphenyl-N, N'-(3-methyl phenyl)-1, 1'-biphenyl-4, 4'diamine], is deposited as a hole-transporting film on the transparent electrode 33 by the cluster ion beam (ICB) method and, then, an emitter material such as anthracene is deposited on this hole transporting film by the ICB method, and, on this emitter material layer, a perylene tetracarboxylic acid derivative is deposited as an electron-transporting film by the ICB method, thus forming the molecular film 32 having a light-emitting function.

Finally, formed on the electron transporting film are Mg electrodes which serve as the electrodes 31. The wiring leads 35 are formed by vacuum evaporation of a metal such as aluminum and are connected to the Mg electrodes.

Next, the operation of the above device will be described. In a neuro-network, a signal input to a neuron is coupled to a signal output from another neuron before the input signal is supplied to that neuron. Such a coupling affects an input condition for the neuron to which the input signal is supplied. However, it does not follow that the outputs of all the neurons affect one neuron. By determining the manner in which the output of a neuron affects an input to another neuron in accordance with the information to be processed, the input information can be processed at high speed and with high efficiency. This embodiment utilizes the photoconductivity of the molecular film 12 and the light-emitting function of the molecular film 32. That is, light signals from the molecular film 32 are received by the molecular film 12, and the Tij portions 16 transmit signal output from the neurons 11 based on a change in conductivity of the molecular film 12. In other words, since the output wiring lines 14 on the molecular film 12 and the input wiring lines 13 therebelow are interconnected, by applying a light pattern on the molecular film 32 to the Tij portions 16 as a matrix signal, a high efficiency information processing as mentioned above can be realized. Further, in the Tij portions 18, currents flowing between the output wiring lines 14 and the input wiring lines 13 can be controlled in accordance with the intensity of light. That is, the resistance in the Tij portions 16 can be changed according to the intensity of light, so that, in addition to an ON/OFF digital pattern formed by the matrix section 32, changes in voltage applied between the electrodes 31 and 33 can be utilized as optical signals to be supplied to the Tij portions 16, thereby making it possible to realize an information processing which is still more efficient than in the case where binary Tij values are used. Further, since a Tij pattern is prepared by optical writing as described above, the rewriting of Tij pattern can be achieved, thus making it possible to realize an information processing of a higher level than in the case where a Tij pattern is fixed.

By changing a Tij pattern and Tij resistance in accordance with output signals, it is also possible to impart a learning function to information processing.

FIG. 3(a) is a wiring diagram showing an information processing device in accordance with another embodiment of the present invention, and FIGS. 3(b) and 3(c) are sectional views taken along the lines A--A' and B--B', respectively, of FIG. 3(a). In the drawings, the components which are identical with or equivalent to those of FIGS. 2(a) and 2(b) are referred to by the same reference numerals and a description of such components is omitted here. The device shown includes output electrodes 20, input electrodes 21, and wiring lines 22 and 23 on the first layer of molecular film 12. The wiring lines 22 are positioned above the output electrodes 20, and the wiring lines 23 are positioned above the input electrodes 21. The reference numerals 24 and 24' indicate wiring lines on the second layer of molecular film 12'; the reference numerals 25 through 28 indicate positions to be irradiated with light; and 29 indicates a neuron spaced away from the neuron 11.

Next, a method of producing the device of this embodiment will be described.

Neurons 11 and 29 which consist of analog or digital circuits formed so as to simulate a neuronic operation in a living body, are arranged in matrix form on one surface of a silicon substrate 17 by the integrated circuit technique. Then, by vacuum evaporation of a metal such as aluminum, the output and input electrodes 20 and 21 of the neurons are formed on the integrated circuit. The remaining portions of the surface of the integrated circuit where no electrodes are formed are covered with an insulating film such as the SiO.sub.2 film 18, thereby leveling the circuit surface. On this wafer thus formed, the first layer of molecular film 12 having heterojunction is formed by the Langmuir-Blodgett method in the same manner as in the embodiment shown in FIGS. 2(a) and 2(b). Semitransparent aluminum wiring lines 22 and 28 are formed on this first layer of molecular film 12 such as to respectively extend just above the output electrodes 20 and the input electrodes 21 of the neurons 11 aligned in lateral rows. Afterwards, the second layer of molecular film 12' is formed in the same manner as the first layer of molecular film 12. Then, semitransparent aluminum electrodes 24 and 24' are formed, two for each neuron, on the second layer of molecular film 12' such as to extend above the neurons 11 aligned in longitudinal rows but not to overlap the output and input electrodes 20 and 21 of these neurons. The elements of the light-emitting sections 81 through 85 are formed in the same manner as in the case of the device shown in FIGS. 2(a) and 2(b).

Next, the operation of the above device will be described. For example, the output of the neuron 11 in the upper left corner and the input of the neuron 29 in the right bottom corner of FIG. 8(a) are interconnected in the following manner. A plurality of rays of light irradiate those sections of the device shown in FIG. 3(a) where neuron electrodes and wiring lines cross each other. When, for example, an intersection point 25 of the output electrode 20 of the upper left neuron 11 and one of the wiring lines 22 formed on the first layer of molecular film 12 is irradiated, this output electrode 20 and this wiring line 22 are electrically interconnected, thus transferring an electrical signal on the output electrode 20 to the wiring line 22. Then, when an intersection point 26 of the wiring line 22 and one of the wiring lines 24' formed on the second layer of molecular film 12' is irradiated with light, the above wiring line 22 and this wiring line 24 are electrically interconnected, thus transferring the electrical signal on the output electrode 20 of the neuron 11 to the wiring line 24'. When an intersection point 27 of the wiring line 24' and the wiring line 23 which is on the first film layer of molecular film 12 and extends above the input electrode 21 of the neuron 29 is irradiated with light, the wiring line 24' and this wiring line 23 are electrically interconnected, thereby transferring the electrical signal from the output electrode 20 of the neuron 11 to this wiring line 23. Finally, when an intersection point 28 of the wiring line 23 and the input electrode 21 of the neuron 29 is irradiated with light, the wiring line 23 and this input electrode 21 are electrically interconnected, thus allowing the electrical signal from the output electrode 20 of the neuron 11 to be transferred to the input electrode 21 of the neuron 29.

Thus, by simultaneously irradiating the four points of intersection 25, 26, 27 and 28 with light, the output of the neuron 11 can be coupled to the input of the neuron 29. Such a coupling relationship can be applied to other neurons, thus making it possible to express all the input/output couplings between the neurons.

FIG. 4 is a characteristic chart showing an example of the photoconductivity of the molecular film 12 and 12'.

Thus, an information processing device of this invention comprises a semiconductor integrated circuit section simulating a neuronic function of neural network, and a molecular film device provided on the integrated circuit section and having a photoelectric function, Tij portions of a plurality of neuronic circuit regions provided on the integrated circuit section being written by light. Due to this construction, the writing of the Tij matrix can be performed arbitrarily, and the number of wiring lines can be reduced. Accordingly, an information processing device can be obtained which performs information processing with high efficiency and provides a high level of integration of neurons.