1968 INTERNATIONAL ELECTRON DEVICES MEETING 253

lated in the analog model by shortening the RC network piece by piece. The currents at the moving borders of the network are reduced similar to the decreasing diode cur- rent during the decay period. Using this analog model the reverse recovery process of diodes with arbitrary doping profiles in the middle region can be investigated. The model yields terminal properties and some quantities in the interior of the device, such as carrier densities and particle currents, as function of position and time. Results on the influence of forward and reverse cur- rents, doping profile, width and carrier lifetime in the middle region are reported.

4) A Sic Backward Diode-R. FarreJl, NASA Electronics Research Center, Cam- bridge, Mass. The development is reported of Sic

backward diodes, to our knowledge the first devices of this kind. The diodes are fabricated by alloying at 2100O Si to a -S ic doped with AI (1020 cm-8) in a nitrogen atmosphere. Following lead attachment we reduce the junction area by electrolytic etching.

A typical I-V characteristic shows a conduction knee at a few tenths of a volt in the high-conduction (tunnel) direction, and a “reverse” (injection) current of the order of 10 mA at two volts for a junction area of about lo+ cm2.

The device has already been operated over a temperature range from 78 to over 900’K with no apparent degradation. Although the device was originally conceived as a microwave detector and mixer, pre- liminary measurements on large-area ver- sions suggest interesting capabilities for applications requiring low-voltage, high- frequency rectification over a very wide temperature range.

Electrical and metallurgical junction characterization are given in detail as well as fabrication techniques and X-band detec- tion performance.

5 ) A Thin-Film Diode Strain Sensor- R. M. Moore and C. J . Busanovich, RCA Laboratories, Princeton, N. J . A new type of thin-film strain sensor has

been conceived. This sensor is a p-n hetero- junction diode utilizing polycrystalline semiconductor layers obtained by vacuum evaporation onto an insulating substrate. The device exhibits large shifts in its for- ward I-V characteristic when subjected to a mechanical strain, and thus functions as a low output impedance voltage source.

Typical test devices have a junction area of 0.12 cm2 and are fabricated on standard microscope slides. Their forward resistance is 50 ohms at a bias of 10 mA and 1.5 volts. They exhibit a voltage sensitivity of 500 volts per unit strain a t this bias with an applied strain of 5XlO-‘. This corresponds to a gauge factor of loa as compared to a maximum of about 200 for single crystal semiconductor strain gauges (piezoresis- tive), and 3 for metal strain gauges,

A particular advantage of this new type of diode strain sensor is that it can be formed on a variety of insulating substrates; thus far, units have been fabricated on extremely flexible substrates such as mica, Mylar, and

Kapton. This freedom of choice in substrate material makes it possible to tailor the mechanical characteristics of the sensor support structure to fit the particular appli- cation without the use of mechanical im- pedance matching structures.

I t is postulated that this new type of strain sensor operates via the mechanism of a piezoelectrically induced field-independent polarization discontinuity at the interface of the p-n heterojunction. An experimental

establish the validity of this hypothesis. investigation is presently under way to

Most of the units fabricated and tested have used an n-CdSelp-Se combination, but a variety of other semiconductors and semi-insulators from the 111-V and 11-VI compounds are suitable.

Session 20-Electron Tubes IV: General Electron Devices Chairman: G. Taylor Organizer: J. S. Needle

1 ) An Ultra-Low-Noise X-Band Signal Source-C. €3. Searks , Sperry Electronic Tube Division, Gainesville, Fla. This paper describes the various steps

taken in a program to provide a 500-mW X-band signal having state-of-the-art signal purity, Le., one with the least possible AM and FM noise. The design and performance of the final device, a high-voltage convec- tion-cooled Ion-noise two-cavity klystron oscillator matched to a high-Q external stabilizing cavity, is described.

Final evaluation required an improved method of measuring both AM and F M noise, as the device performance was below the measurement threshold of available noise-measuring equipment. Details of the measurement method are also discussed briefly.

A stabilization factor of 12 was achieved, using a stabilizing cavity with a Qo of 55 000. Insertion loss was approximately 10 dB. Output power was in excess of 600 mW, at 9715 MHz. FM noise was less than 0.0007 Hz in any 1-Hz bandwidth for all modulation frequencies above 5 kHz. The corresponding AM noise level was more than 150 dB below the carrier in any 1-Hz band- width.

2 ) Gas Discharge Switches for S- and X- bandl-H. Goldie and M . A . Goldman, Westinghouse Defense and Space Center, Baltimore, Md. 1) A broad-band plasma waveguide

switch has been developed which provides greater than 100 dB isolation when active and less than 0.2 dB insertion loss when passive. The cold loss is under 0.1 dB over the mid 10 percent frequency band. The turn-on time is 100 ns and the turn-off time is 120 ms. The absorbed switch power (arc loss) was measured and found to be negli- gible under conditions of high ionizing beam strengths and moderate plasma densities. The operation of the switch is very similar to gas thyratrons except that the grid is re- placed by a perforated waveguide with no internal resonant structures. Consequently,

1 Sponsored by Laboratories, N. C0066.

Y.. the U. S. Naval Applied Science

under Contract N00140-57-

the device can be simultaneously used as a fail-safe receiver protector and switchtube in (magnetron source) radars; the hybrid nature provides receiver isolation (k 100 dB) during transmit time since the switch- tube must be conducting in order for the magnetron to oscillate. Experiments have shown feasibility of this class of operation.

Prototype switches are 2.5 inches long, fullv hardbrazed, and are processed using high-temperature bakeout techniques, re- quired drive power included a 500-volt 40-mA anode supply, 6.3-volt cathode and reservoir heaters, and a 100-volt 0.5-ps trigger circuit. Experimental results are presented.

2) Experimental gas discharge limiter stages were built using the soft-beta emitter tritium as a priming electron source. The isotope is adsorbed in a titanium film evaporated onto a metal substrate in the form of a button or foil. The radioactive source is located near or a t the microwave discharge gap. Firing power on single-cone and double-cone X-band limiter stages is presented for a variety of button and foil configurations and gas fills. Results of ionization chamber measurements of cur- rents available from the radioactive source buttons and foils are presented for a variety of fills. A source providing a beta current of 7 X 10-’1 amperes in vacuum typically provided 10V amperes in a low-pressure gas environment. Measurements of an X-band limiter stage using the radioactive source and a gas fill of 12 torr water plus 6 torr krypton had a stable firing power threshold of 6.6 watts with a matched load terminating the line, and 2.6 watts with a short as the termi- nation. The short simulates the load if the stage is followed by a diode limiter.

3) Harmonic Generation in TR Discharges‘ -H. S. Maddix, dlicrozlaoe Associates, Burlington, Mass. With increasing use of higher sensitivity

detection for both radar and communica- tions applications, there exists an increasing need for reduction in intersystem interfer- ence and the control of spurious signal generation. Normally the duplexer is not considered a contributing source to spurious radiation; however, there has been found evidence of increased spurious signal genera- tion resulting from installation of duplexers in some systems. The spurious signals ap- pear generally as harmonics of the trans- mitted frequency.

Field reports of spurious radiation have been verified in a laboratory investigation. At L-band peak harmonic powers as high

at a peak power of 400 kW. At X-band, a as 25 watts were observed from a discharge

peak second-harmonic power of 2.5 watts was observed from a discharge at 1.5 kit’ peak power. Conversion loss varied from 28 to 70 dB depending primarily upon pressure. Harmonic power was radiated in a series of Tonks-Dattner electroacoustic resonant peaks which varied with incident power and pressure.

I t was found that conventional TR tubes

tronics Systems Command under Contract N00024- 1 This research was supported by the Naval Elec-

67-C-1313.