Fabrication and characterization of polymeric three-axis thermal accelerometers

Abstract

The concept, fabrication process, and characterization of a three-axis thermal accelerometer are presented in this paper. A combination of microelectromechanical systems (MEMS) technology with microinjection molding enables the realization of functional, highly complex 3D geometries at the microscale, used here for the fabrication of a fully integrated three-axis accelerometer. While conventional thermal accelerometers are silicon based, using MEMS technologies only, the integration of polymeric materials and technologies into the fabrication process can greatly improve the realization of three-axis devices while diminishing the typical thermal losses. Three-axis thermal accelerometers were successfully fabricated by combining the proposed technologies proving the viability of the concept. Fabricated accelerometers show xy-axis sensitivity around 8 mV g−1, a z-axis sensitivity of 2.2 mV g−1 for a power of 45 mW and a 4 Hz bandwidth (bandwidth is based on simulations). Thermal tests performed showed that the heater can sustain up to 280 °C without overheating the remaining structures and damaging the device.

Tri-axis convective accelerometer with closed-loop heat source

“…11 and 12), the effect of the Z acceleration can be cancelled out easily by means of a conventional electric circuit such as by forming half Wheatstone bridge by the pair of X hotwires. This kind of circuit is common in use in various sensing techniques, as reported in numerous literature [37], [39]. Figure 13 shows the variation of the output voltage on the hotwires X with respect to the centrifugal acceleration applied to the X axis by the turntable (see Fig.…”

“…This device allows obtaining the Z sensitivity of 25 µV/g. In the works published by Rocha and Silva [38][39][40][41], a polymeric three-axis device was fabricated by conventional micromachining and injection molding. The heating and the temperature sensing structures, made of aluminum, were patterned on a flexible polymeric membrane.…”

A review of micromachined thermal accelerometers

“…The measured sensitivity were 66, 64, and 25μV/g on the X, Y, and Z-axes respectively, using SF 6 as working fluid at a total heater power of 2.5mW. Later, a novel design consisting of three flexible polyimide membranes (two identical Z-axis membranes on either side of a central membrane) encapsulated within four polymeric microparts was reported, as seen in figure 6 [47], [48]. The central membrane included the heater and temperature sensors for X and Y-axes, while the upper and lower membranes had sensors for Z-axis.…”