We have designed and fabricated a surface micromachined Pirani pressure sensor with an extremely narrow gap between its heater and heatsink (substrate) with superior output linearity in the atmospheric pressure range. The gap size of the device has been reduced to 50 nm by using a layer of PECVD amorphous silicon as a sacrificial layer and a xenon difluoride (XeF 2 ) gas phase etching technique. Such a narrow gap pushes the transition from molecular to continuum heat conduction to pressures beyond 200 kPa. The higher transition pressure increases the measurement range and sensitivity of the gauge in atmospheric pressures. The gas phase etching of the sacrificial layer eliminates stiction problems related to a wet etching process. The active area of the sensor is only a 6 × 50 μm 2 microbridge anchored to the substrate at both ends. An innovative fabrication technique was developed which resulted in a virtually flat microbridge with improved mechanical robustness. This process enabled us to have a very well-controlled gap between the microbridge and the substrate. The device was tested in a constant heater temperature mode with pressure ranges from 0.1 to 720 kPa. The heater power was only 3 mW at 101 kPa (atmospheric pressure), which increased to about 8 mW at 720 kPa. The output sensitivity and nonlinearity of the device were 0.55% per kPa at 101 kPa and ±13% of the output full scale, respectively.

No abstract

No abstract

The operational principle of a thermal MEMS (Micro Electro-Mechanical Systems) gyroscope was reported in Hilton Head 2010 [1]. In the current work we describe two factors that can produce a spurious rotation signal in gyroscopes of this type. These factors are, firstly, distortion or asymmetric placement of the heating elements or temperature sensors; secondly, the effects of linear acceleration and/or gravity on the fluid flow inside the device, and hence on the gyroscope output. In order to simulate the thermal gyro and the origin of these spurious signals, a mathematical model is built and developed through the COMSOL CFD package. The spurious signals predicted by this simulation are shown to correspond to experimental measurements. Alternative cavity shapes are investigated and simulated as a mean of suppressing the spurious signal.

This paper introduces an innovative sacrificial surface micromachining process that enhances the fabrication of freestanding microstructures and compliant mechanisms. This process eliminates the topography issues related to the fabrication of these microstructures and achieves planarization without using Chemical-Mechanical Polishing (CMP). The process is based on the silicide technology, which is low temperature and post-CMOS compatible. We use a layer of amorphous silicon (a-Si) as the sacrificial layer. High etch selectivity between silicon and nickel silicide in the XeF 2 gas enables us to use the silicide to anchor the structures to the substrate. To anchor the structure, the a-Si over the structure's anchor is converted to the nickel silicide. The silicide layer has the same thickness as the sacrificial layer, producing a virtually flat freestanding structure. The maximum measured step between the anchor and the sacrificial layer was about 4nm on a 100nm thick sacrificial layer.