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ABSTRACT: A micromachined silicon subminiature microphone based on
piezoelectric P(VDF-TrFE) films spin-coated on top of silicon nitride
membranes is presented. The residual tensile in-plane-stress is
minimized by an additional boron implantation as well as by using a
stress compensated layer system of silicon dioxide and silicon nitride.
Spin-coating and corona poling of 70/30-P(VDF-TrFE) is described as well
as important properties of these layers. The acoustic measurements were
done on-wafer and yielded a sensitivity of 0.21 mV/Pa and therefore an
equivalent noise level of 54.6 dB(A). The bandwidth is about 17 kHz, and
the total harmonic distortion is less than 1.8% even for 127.5 dBSPL
Electrets, 1996. (ISE 9), 9th International Symposium on; 10/1996
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ABSTRACT: In this paper a silicon subminiature microphone is described,
which is based on the piezoelectric effect of spin-coated
P(VDF/TrFE)-layers. The polymer layers are placed on top of a very thin
silicon nitride membrane, which is implanted with boron ions in order to
reduce the tensile stress of the diaphragm, resulting in higher
microphone sensitivities. A maximum sensitivity of 150 μV/Pa, a
bandwidth of about 16 kHz and an equivalent noise level of less than 60
dB(A) were measured. Considering the small area of the membrane of the
microphone (1 mm<sup>2</sup>), the sensors show a much better
performance than former microphones with piezoelectric polymer layers
Electrets, 1994. (ISE 8), 8th International Symposium on; 10/1994
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ABSTRACT: Corrugated electret membranes are used in a micromachined silicon microphone. The membranes consist of a permanently corona-charged double layer of silicon dioxide and silicon nitride, known to have excellent charge-storing properties. This electret can replace the external bias needed for condenser microphones. The well-known LOCOS technique—also combined with dry etching—is used for the first time to fabricate membranes with corrugation depths of several microns. The membrane thickness amounts to 600 nm.The interferometrically measured center deflection is up to 40 nm/Pa for diaphragms with four corrugations of up to 3.3 μm depth and a size of AM=1 mm2. This high mechanical sensitivity limits the dynamic range to sound pressures below 50 Pa. The obtained mechanical sensitivities are in excellent agreement with the theory.The most compliant corrugated diaphragms result in a microphone sensitivity of 2.9 mV/Pa, an equivalent noise level of 39 dB(A) and a total harmonic distortion below 1.7% at 28 Pa (123 dB SPL). The corrugation depth in the sensors has been only 1.3 μm. All sensors cover the whole audio and low ultrasonic range. The temperature coefficient is between 0.05 and 0.1 dB/K.
Sensors and Actuators A: Physical.
