Fabrication of integrated pressure-flow-temperature sensor for hydraulic systems

This work develops a low cost multi-functional micro-electro mechanical systems (MEMS) sensor for use in fluid power systems. The device is small to facilitate easy integration into fluid power components, and has the capability to sense system pressure, fluid temperature, and small pressure differences that can be correlated to flow rate. The design of each of the sensing aspects of the device is outlined, as well as their layout on the sensor die. Pressure sensing with the device is accomplished through the use of polysilicon piezoresistors, while temperature sensing is accomplished using polysilicon thermisters. The procedure necessary to fabricate prototype units is illustrated in detail, and special processes noted. Performance characteristics of prototype sensors compare well to design model predictions. The polysilicon thermister demonstrated a linearity of 2.32%, a repeatability of 0.6%, and an accuracy of 1.5°C. The differential pressure sensor demonstrated a linearity of 0.4%, a repeatability of 0.13%, and an accuracy of 3.6%. The system pressure sensor demonstrated a linearity of 0.7%, a repeatability of 0.3% and an accuracy of 4.2%. These performance characteristics prove the functionality of the device.