Microsensor with Piezoresistive Diamond Sensing Elements

摘要

A prototype of a novel diamond (p-D) monolithic pressure sensor, operational atthe present stage up to 580 deg F, was developed and characterized. The work consisted of research and development directed toward design, fabrication, packaging, and testing of the sensor. The scope of the program could be divided into two sets of interrelated goals: objectives indirectly associated with the program and objectives directly associated with the program. Measurements of the gage factor (GF) of the polycrystalline diamond film conducted up to 880 deg F revealed that the factor increases linearly from approx. 5 at room temperature to approx. 50 at 780 deg F. It is for the first time that values of the gage factor of polycrystalline diamond film as a function of elevated temperatures are known to be reported. The temperature coefficient of resistance (TCR) measurements were conducted on the beam strain gages, as well as on the film strain gages in the range of temperatures between 80 deg F and 1180 deg F. A successful procedure was developed for depositing intrinsic diamond film, several microns thick, on SiC. The p-diamond was doped 'in situ' during the deposition with a boron compound source. A new, more efficient process to pattern diamond was developed. This new process for resistor fabrication can be applied to produce resistors in p-diamond doping of any doping level. Two ohmic contact metallization schemes (Pt and Ti/Pt) were selected to provide electrical connection to the external electronic instrumentation. A new passivation technique, which enabled oxidation resistance of the diamond at 800 deg C and above, was developed. Processes associated with the fabrication of p-diamond resistors were refined. To form the force collector (diaphragm), a two stage etching process was utilized.