This paper describes the measurement results of piezoelectric harvesters with AlN as piezoelectric material. The output power harvested from mechanical vibrations has been measured on micromachined harvesters with different geometries. The resonance frequencies ranged from 200 up to 1200 Hz. A maximum output power of 60 µW has been measured at an acceleration of 2.0 g at a resonance frequency of 571 Hz; the power output is of the same level as obtained with devices based on PZT. The package of the harvester requires special attention, since air-damping can significantly decrease the maximum power output.
This paper describes the characterization of thin-film MEMS vibration energy harvesters based on aluminum nitride as piezoelectric material. A record output power of 85 μW is measured. The parasitic-damping and the energy-harvesting performances of unpackaged and packaged devices are investigated. Vacuum and atmospheric pressure levels are considered for the packaged devices. When dealing with packaged devices, it is found that vacuum packaging is essential for maximizing the output power. Therefore, a wafer-scale vacuum package process is developed. The energy harvesters are used to power a small prototype (1 cm 3 volume) of a wireless autonomous sensor system. The average power consumption of the whole system is less than 10 μW, and it is continuously provided by the vibration energy harvester.
The process of photoanodic etching of deep pores in lightly doped n Ϫ -Si wafers was investigated. On a 6 in. wafer, more than 1 billion pores, regularly distributed over the wafer in a hexagonal array with a pitch of 3.5 m, were obtained using an electrolytic back contact. The diameter of the pores was about 2 m and depths up to 400 m could be achieved. Kinetic experiments revealed that the etching process was diffusion controlled in a solution containing HF, H 2 O, and ethanol. Electrochemical experiments showed that H 2 evolution took place at the back side of the Si wafer and that H 2 and O 2 evolved at the Pt cathode and anode, respectively.
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