Microstructure sensors

Surface micromachined polysilicon pressure sensors offer an attractive, cost-effective high-performance technology if material repeatability issues can be solved. The pressure ranges over which these devices are designable have been established and are set by the maximum allowable diaphragm stress and the minimum acceptable output level. The low pressure limitation can be eliminated by improving the transducer sensitivity. The substitution of the resonating force sensor, another polysilicon component, for piezoresistors can accomplish this but complicates processing. This approach is justified for high performance applications. The alternative is found in a differential transducer which is furnished with double-sided over-pressure stops. One of these stops is provided by the silicon substrate, the other by an electroplated air bridge which is formed by X-ray lithography and electroplating in the presence of a sacrificial layer. The end result is a rigid, thick, accurately spaced stop which results in devices which are rugged and can measure differentials in the 1" water range.<>