Millimeter-Wave Power Limiter

This invention relates generally to semiconductor power control devices and more particularly to a semiconductor switch device adapted to control the flow of RF power propagating along a waveguide structure.

When operating an image line transmitter and receiver in a high power signal environment, there is the attendant problem of protecting the mixer stage of the front end section of the receiver from other high average power emitters in close proximity. Most conventional power limiting devices operating, for example, in the microwave range are fabricated around a nonlinear element, generally a ferrite or diode in a coaxial or waveguide structure. Such devices are well known to those skilled in the art. In the approach to millimeter wave and submillimeter wave components; however, it has become apparent that the techniques used in the microwave region are inapplicable.

It is an object of the present invention, therefore, to provide a power limiter for millimeter waves.

It is another object of the present invention to provide a semiconductor millimeter wave power limiter.

Yet another object of the present invention is to provide a bulk effect millimeter wave power limiter adapted to protect RF receiver apparatus.

Still another object of the present invention is to provide a RF power limiter in the form of planar PIN beam lead diode formed on a dielectric image transmission line.

Briefly, these and other objects are provided in accordance with a dielectric image transmission line for millimeter waves consisting of a gallium arsenide waveguide structure which additionally acts as a substrate on which is formed a bulk effect beam lead PIN diode consisting of relatively thick epitaxial layers of heavily doped n and p regions of semiconductor material separated by an intrinsic region generally in the form of a wedge lying transversely relative to the longitudinal direction of the gallium arsenide image line. The doped regions of n and p semiconductor material are formed as opposing recessed regions in adjoining side edges of the wedge or intrinsic material. On the application of a predetermined bias and signal potential across the diode an avalanche effect will occur at a predetermined power level which operates to limit the power flow of RF energy along the gallium arsenide millimeter-wave image waveguide and thereby protect any circuitry beyond the location of the PIN diode.

FIG. 1 is a perspective view of a first embodiment of the subject invention;

FIG. 2 is a perspective view of a second embodiment of the subject invention;

FIG. 3 is a top planar view partially in schematic form of the embodiment shown in FIG. 2 and being illustrative of its operating mode;

FIG. 4 is a side planar view partly in schematic form of the embodiment shown in FIG. 2 and being further illustrative of its operating mode; and

FIG. 5 is a graph helpful in understanding the operation of the subject invention.

Referring now to the drawings and more particularly to FIG. 1, reference numeral 10 designates a dielectric image transmission line consisting of a waveguide structure comprised of a Group III-V compound, preferably gallium arsenide (GaAs). Although GaAs has a relatively high resistivity and is therefore semi-insulating, it nevertheless is adapted to propagate electromagnetic energy in the millimeter and sub-millimeter frequency region with relatively low loss and accordingly can be operated as a dielectric image line for RF power. On the upper surface 12 of the GaAs image waveguide 10 is formed a wedge-shaped semiconductor PIN diode having a planar configuration which uses the GaAs waveguide as a substrate. The PIN diode consists of a wedge-shaped region of intrinsic semiconductor material 16 into which is formed along the intersecting side edges 18 and 20 opposing recessed regions 22 and 24 of opposite semiconductivity type which are respectively heavily doped with n and p type dopant materials. Connected to the n and p regions 22 and 24 are a pair of planar beam leads 26 and 28 which extend outwardly from the PIN diode longitudinally along the substrate surface 12. The planar structure of the PIN diode 14 is formed from relatively thick epitaxial layers which are sequentially grown in the planar format shown using either chemical vapor deposition or molecular beam epitaxy, methods well known to those skilled in the art. Such a configuration permits its integration into other components such as the front end of an RF receiver, not shown.

A modified form of the embodiment shown in FIG. 1 is disclosed in FIG. 2. There a planar PIN diode is formed on the surface 12 of the substrate 10 as before, however, the configuration shown in FIG. 2, in addition to the intrinsic region 16, now includes respective contiguous n type and p type semiconductive regions 30 and 32 which extend outwardly from the inwardly disposed or recessed n and p doped regions 22 and 24 along the side edges 18 and 20. Such a configuration in certain instances is easier to fabricate inasmuch as relatively wide contact surfaces 34 and 36 are provided for mating with adjoining beam leads 26' and 28' which are shown extending across the width of the upper surface 12 rather than lengthwise as shown in FIG. 1.

In either case, the two opposing recessed n and p regions 22 and 24 are separated by intervening intrinsic material of region 16. In operation, as shown in FIGS. 3 and 4, a DC bias voltage is adapted to be applied across the PIN diode configuration 14' by means of voltage terminals 42 and 44 coupled to the beam leads 38 and 40, respectively, which act as ohmic contacts. Additionally, an inductance element 46 is included between the terminal 42 and the beam lead 38 for operating as an RF frequency choke. The application of the DC bias voltage across terminals 42 and 44 is adjusted so that a portion of the neutral impurities in the intrinsic region 16 between the n and p regions 22 and 24 are pre-ionized. The conductivity of the PIN diode is adapted to control the RF signal propagating along the GaAs image waveguide 10 in accordance with a control or modulating signal coupled to the intrinsic region 16 along the base edge 21 of the wedge 16 via terminal 48. The DC bias level and modulating signal is adapted to control the RF signal propagation through the GaAs guide 10 in the region of its acting as a substrate for the PIN diode 14' in the following manner. With reference to FIG. 5, curve portion 50 of the RF power in vs. RF power out characteristic shown indicates that above a critical power level Pc, the RF power output is limited to a predetermined value while at relatively low power levels, the RF power propagates through the dielectric waveguide with very little loss. At the limiting critical power level P.sub.c, the energy imparted to the electrons and the holes of the PIN diode 14' is enough to create a net gain in energy causing an avalanche breakdown in the diode whose conductivity increases rapidly with a consequent decrease in dielectric constant whereupon RF energy propagating along the substrate waveguide 10 will be reflected back towards the source, not shown. Accordingly, the modulating or control signal applied to terminal 48 in conjunction with the bias voltage applied across terminals 42 and 44 is adapted to establish the critical power level P.sub.c. When a switching action takes place, power limiting will occur and such action acts to protect any relatively sensitive components which would otherwise be damaged or otherwise rendered inoperative further along the RF transmission line.

Thus what has been shown and described is an RF millimeter wave power control switch in the form of a bulk effect beam lead planar PIN diode structure formed on a substrate of gallium arsenide which is the dielectric image transmission line for millimeter wave propagation.

While the invention has been particularly shown and described with reference to what is at present considered to be the preferred embodiments thereof, it is to be understood from the foregoing that this disclosure is made for purposes of explanation and not limitation and therefore other changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.