SiC Temperature, Acceleration, Pressure and Strain Sensors Project

SiC TAPS

SiC Double-ended tuning fork for strain measurements.

Project Overview

The goal of this research program is to develop a sensor module suite using MEMS-based silicon carbide (SiC) devices. The sensor suite will include temperature, acceleration, pressure and strain sensors that will be suitable for integration with silicon carbide interface circuits for extreme harsh environment applications.

Background

SiC has a wider band-gap, higher breakdown field, and higher thermal conductivity in comparison to Si. These properties make SiC ideal for high temperature, power, and radiation applications. In addition, the mechanical properties of SiC, such as high acoustic velocity, toughness, and chemical inertness are favorable for high frequency MEMS sensors that operate in corrosive environments.

 

Due to the attractive electrical and mechanical properties of SiC, this material will be used to develop TAPS sensors for extreme harsh environments. A complete family of three distinct SiC deposition processes will be developed, each with a different deposition temperature range. This allows SiC electronics to be topped with SiC MEMS structures, and in turn, topped by SiC encapsulation (Figure 1). The deposition temperatures of the three SiC deposition processes will be staged (1200-1600 °C, 750-850 °C, 200-450 °C) so that the deposition process of each successive layer does not violate the thermal budget of the layers below. The TAPS sensor module aims to ultimately resolve 0.01 µ-strain, operate with a bandwidth of 10 kHz, survive temperature excursions up to 600 °C, survive wet steam/hydrocarbon ambient, and withstand 100,000 g-force shocks.

 

Initial work is focused on creating a functioning Double-Ended Tuning Fork strain sensor using the same oscillator scheme implemented in polysilicon [1] as well as an alternative capacitive strain sensor. To overcome relatively high film resistances, variations in sensor design [2], metallization, and fabrication process are also being explored. Optimization of thin-film and bulk etching chemistries and deposition are also ongoing.

 

[1] KE Wojciechowski, B Boser and AP Pisano, “A MEMS Resonant Strain Sensor Operated in Air” MEMS ’04 pp. 841-845 (2004)

[2] SA Bhave, D Gao, R Maboudian and RT Howe, “Fully-differential Poly-SiC Lame-mode Resonator and Checkerboard Filter” MEMS ’05 (2005)

[3] M.B.J. Wijesundara, D.C. Walther, C.R. Stoldt, K. Fu, D. Gao, C. Carraro, A.P. Pisano, and R. Maboudian, “Low Temperature CVD SiC Coated Si Microcomponents for Reduced Scale Engines” Proc. IMECE, Washington D.C., November 15-22, 2003.

[4] D. Gao, R.T. Howe, and R. Maboudian, "High-selectivity Etching of Polycrystalline 3C-SiC Films using HBr-based Transformer Coupled Plasma," Applied Physics Letters, 82 (11), 1742 (2003).

 

 

 

Thin-film SiC etch profile [4].

Thin-film SiC coated rotors [3].