A Micromachined Capacitive Pressure Sensor Using a Cavity-Less Structure with Bulk-Metal/Elastomer Layers and Its Wireless Telemetry Application

Abstract

This paper reports a micromachined capacitive pressure sensor intended for applications that require mechanical robustness. The device is constructed with two micromachined metal plates and an intermediate polymer layer that is soft enough to deform in a target pressure range. The plates are formed of micromachined stainless steel fabricated by batch-compatible micro-electro-discharge machining. A polyurethane roomtemperature-vulcanizing liquid rubber of 38-μm thickness is used as the deformable material. This structure eliminates both the vacuum cavity and the associated lead transfer challenges common to micromachined capacitive pressure sensors. For frequency-based interrogation of the capacitance, passive inductor-capacitor tanks are fabricated by combining the capacitive sensor with an inductive coil. The coil has 40 turns of a 127-μm-diameter copper wire. Wireless sensing is demonstrated in liquid by monitoring the variation in the resonant frequency of the tank via an external coil that is magnetically coupled with the tank. The sensitivity at room temperature is measured to be 23-33 ppm/KPa over a dynamic range of 340 KPa, which is shown to match a theoretical estimation. Temperature dependence of the tank is experimentally evaluated.

Theoretical and experimental investigation of the trapped air effect on air-sealed capacitive pressure sensor

“…In general, a vacuum-sealed capacitive pressure sensor is advantageous for its lower temperature sensitivity and high pressure sensitivity compared to a gas-sealed one. However, it has major limitations such as fabrication and maintaining hermetic high vacuum sealing of the cavity and electrical connection between the vacuum-sealed cavity and the outside of the cavity [3][4][5]. A lot of work has been done to solve these problems, but it is still difficult to obtain and maintain high vacuum level and electrical connection of electrodes [6][7][8].…”

“…Moreover, a further study is needed to assess the effect of additional gas chamber on the performance of a gas-sealed pressure sensor. Another approach to avoid the problems mentioned above was presented by Takahata [5] introducing a cavity-less capacitive pressure sensor. However, this approach is also needed to consider the boundary condition problem and the dielectric property change in the intermediate dielectric layer induced by the applied pressure [14][15].…”

Micro-Electro-Discharge Machining Technologies for MEMS

“…www.intechopen.com configuration relies on the deflection of a relatively thin diaphragm against a sealed cavity, there is concern about the robustness of the diaphragm and leaks in the cavity seal in some applications. This issue has been addressed by devising a configuration consisting of two micromachined metal plates with an intermediate polymer layer, eliminating the need for diaphragms and cavities from the sensor structure (Takahata & Gianchandani, 2008a). Use of polymeric material soft enough to deform in a target pressure range allowed the thickness of the polymer, or capacitance of the parallel plate capacitor, to be dependent on the hydraulic pressure surrounding the device (Fig.…”

Design of Capacitance to Voltage Converter for Capacitive Sensor Transducer

“…There are many research has been done on the sensor transducers using the capacitance to frequency conversion for the past few years. The sensor transducer is suitably used for converting pressure variations (Takahata and Gianchandani, 2008), humidity measurements (DeHennis and Wise, 2005) into corresponding signal with equivalent frequency. Further, such transducers have been used in water level measurement system or even telemetry systems (Mariun et al, 2006;Reverter et al, 2007).…”