Piezoelectric Micro Sensors based on aluminum nitride
Piezoelectric microsystems with aluminum nitride (AlN) have been developed at Fraunhofer ENAS for several years. These microsystems have a high energy density that allows a high miniaturization of MEMS and NEMS. Thus, costs and energy consumption in the fabrication process of the microsystems can be reduced and the variety of possible applications increases. In contrast to the common used lead zirconate titanate (PZT), the aluminum nitride can be integrated in CMOS processes easily. The deposition and patterning of AlN can be realized in conventional equipment for aluminum-based back-end of line technologies. This enables the common fabrication of piezo MEMS and CMOS devices in the same production line. Fraunhofer ENAS and the Center for Microtechnologies of the Chemnitz University of Technology developed the technology to sputter and characterize piezoelectric thin film AlN and integrated the material into silicon-based MEMS and NEMS applications.
Fraunhofer ENAS has various application samples for aluminum nitride-based sensor and actuator systems. The institute introduces a wake-up generator that uses a thin aluminum nitride layer to detect a mechanical event such as acceleration or vibration and converts the mechanical energy into electric energy in order to activate a stand-by system (sleeping system). An acceleration of less than 0.08 g is sufficient to generate enough energy for the wake-up process. The wake-up generator works energy self-sufficiently and without electricity. A system, consisting of ASIC and MEMS requires less than 300 nA current consumption.
These piezoelectric transducers are meeting with great interest in industry as sensor and actuator material. In order to enable these industrial applications, Fraunhofer ENAS, together with the Canadian company Preciseley Microtechnology Inc. and the Saxon medium-sized company EDC Electronic Design Chemnitz GmbH, has developed piezoelectric MEMS that has been successfully integrated as a positon sensor into the industrial mass production technology of the Canadian project partner. Furthermore, the project partners have realized an ASIC for fast, precise and low-noise evaluation of smallest sensor signals. At the Fraunhofer joint stand, Fraunhofer ENAS demonstrated the advantages of aluminum nitride-based systems using a piezoelectric MOEMS. This actuator offers a high scan angle up to 100° at low actuation voltage of less than 20 V and is reliable at temperatures of up to 150 °C.
Additionally, the piezoelectric thin film technology is suitable for operation in liquids. This has resulted in a fluid sensor that can measure and evaluate both viscosity and density of liquids.
There are also applications in the field of inertial sensors, ultrasonic transducers or acoustic emission.