Effect of Mechanical Stress on Polycrystalline Diamond Schottky Diode I-V Characteristics
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EFFECT OF MECHANICAL STRESS ON POLYCRYSTALLINE DIAMOND SCHOTTKY DIODE I-V CHARACTERISTICS G. Zhao*, E. M. Charlson%, E. J. Charlson', T. Stacy, J. Meese, G. Popovici** and M. Prelas** *
Department of Electricaland Computer Engineering, University ofMissouri, Columbia, Missouri 65211
**
Department of Nuclear Engineering, University of Missouri, Columbia, Missouri 65211
ABSTRACT Schottky diodes to be used for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode. At selected values of constant forward biased current, a linear relationship between voltage and stress, for stress less than 10 N was observed. The stress sensitivity of the diode was as high as 0.74 V/N at 1 mA forward bias. This study shows that polycrystalline diamond Schottky diodes are stress sensitive devices and have potential as mechanical sensors. INTRODUCTION In the 1960s, much work was done on the effect of mechanical stress on the current-voltage (I-V) characteristics of silicon and germanium junction diodes and Esaki (tunnel) diodes. 14 Though this effect was of scientific interest, only limited application of these silicon and germanium based diodes was made because they were very vulnerable to damage when high stress was applied. The only reported working device was an experimental silicon microphone consisting of a hard stylus pressing on a silicon diode, 5 which was found to be very susceptible to acceleration-caused irreversible damage. To our knowledge, no practical device of this type has been made on either silicon or germanium because of problems related to material hardness. In the past decade, diamond has received much attention as a promising material due to its unique combination of desirable electrical, optical and mechanical properties. However, both natural and ultrahigh-pressure-synthesized diamond are very expensive, difficult to dope and can only be used to make very simple devices. Recently, various diamond chemical vapor deposition (CVD) processes have been developed, 6 which show great promise in providing the base material for electronic devices. Some polycrystalline diamond devices, Mat. Res. Soc. Symp. Proc. Vol. 270. @1992 Materials Research Society
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in particular Schottky diodes have been made on CVD diamond. 7 1 ° Much effort has been devoted to studying the electrical and optical characteristics of these devices. In this study, a new potential application has been found for the CVD diamond based Schottky diodes, namely, the conversion of mechanical stress into an electrical signal. Boron doped polycrystalline diamond thin films were deposited on p-type silicon substrates using a hot-filament CVD (HFCVD) process with trimethyl borate as an in-situ dopant source. The Schottky diodes were formed using aluminum contacts and then tested to determine the effect of mechanic
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