Measurement: Pressure sensor

New pressure sensor increases stability

Who

GE Sensing has launched a trench-etched resonant pressure sensor (Terps) technology that it says increases accuracy and stability by a factor of 10 over existing piezoresistive pressure sensors, while extending the pressure range capability associated with resonating pressure technology sensors. 

Technology

Terps stems from research into silicon resonating pressure sensors. The silicon structure is driven into resonance by the application of an electrostatic field and when pressure is applied to a diaphragm, the silicon resonator is stretched, changing the frequency, much like a guitar string. This change in frequency relates directly to the applied pressure.

A resonating silicon pressure sensor is more accurate and stable than a piezoresistive device because it exploits the mechanical properties of the single crystalline structure of silicon. The primary benefit is that silicon is elastic to its fracture point which allows the creation of a high-quality resonance sensor, whose frequency stability is unaffected by the electronics in the product. In comparison, piezoresistive technology requires the introduction of resistive elements into the silicon crystal structure, which have unstable electrical properties. The benefits of a resonant sensor are low hysteresis and good long-term stability. The thermal effects are repeatable and can therefore be corrected.

Through the use of deep reactive ion etching it is possible to create complex and arbitrary geometries within the resonating structure. This is necessary to optimise the design and performance of the resonator to make higher pressure and temperature ranges possible. The use of silicon fusion bonding allows for the machining of separate components of the sensor to be processed separately then fused together to retain the properties of single-crystal silicon, again providing greater flexibility in the design of the sensor element and making higher pressure and temperature ranges possible.

These two processes, along with other proprietary design elements such as a new frequency detection method that provides a much stronger signal from the resonator, make it possible to package the sensor element in a way that can be mechanically isolated from the process media through the use of a metallic isolation diaphragm with an oil fill. This is an advance for a sensor of this performance class over other high-accuracy technologies which are typically limited to dry non-corrosive gases. Associated electronics can be further from a Terps sensor, which permits operation in higher temperature environments.

Application

Steve Sajben, product manager for pressure sensors, said: “The technology and manufacturing we have explored and created allow us to produce a pressure sensor with all the inherent accuracy and stability of resonant silicon but with significantly greater capability in terms of pressure range, temperature range, and mechanical packaging.”