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A subminiature condenser microphone with silicon nitride membrane and silicon back plate
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1989
Year
Biomedical AcousticsEngineeringSubminiature Condenser MicrophoneAcoustic SensorNoiseAirborne SoundFabrication ProcessInstrumentationAcoustic CameraAcoustic MethodsAcoustic PropagationNoise MeasurementCapacitive Silicon SensorDistant Speech RecognitionOptical SensorsBiomedical SensorsSensorsSilicon Nitride MembraneTransducer PrincipleSpeech ProcessingUnderwater SensingMicromachined Ultrasonic Transducer
The fabrication process and the properties of a capacitive silicon sensor for the detection of airborne sound are described. The device consists of two chips; one chip carries a 150-nm-thick silicon nitride membrane of 0.8×0.8 mm2 , and the second chip represents a complete back plate including the back electrode and the air gap spacer. Both chips are produced by means of an orientation-dependent etching procedure. The overall dimensions of the transducer are 1.7×2×0.6 mm3 . Measurements of the acoustic properties yield sensitivities between −60 and −90 dB re: 1 V/Pa, depending on the tension of the diaphragm. The most sensitive microphones have a frequency response extending up to 2 kHz, while the less sensitive transducers have higher cutoff frequencies.