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Transcript of MEMS Microphone
Briliant Adhi Prabowo
What is microphone?
Microphone is a device to detect acoustic signal
to electric signal.
- To be amplified.
- To be transmitted.
- To be processed. (audio processing)
- To be stored.
Natural microphone = EAR
Difficult to be transmitted,
stored, processed, amplified
Sound is mechanical wave that oscillated in frequency range around 20 Hz - 20 kHz.
Infrasonic < 20 Hz
Ultrasonic > 20 kHz
- Sound vibrates membrane.
- Membrane convert the vibration to electrical signal
Acoustic vibration to
Microphone device - integrated in a single chip - fabricated using CMOS technology.
Previous technology : electret condensor microphones (ECS) - assembled from discrete parts.
Type of MEMS Microphones
Analog MEMS Microphones
convert a sound pressure input into an analog voltage output.
Digital MEMS Microphones
convert a sound pressure input into a digital output signal, typically in pulse density
modulation format (PDM).
MEMS Microphone Principle
- There is a voltage between membrane and back-plate.
- A capacitance is occurred in membrane-plate.
- Membrane is vibrated by sound wave.
- Capacitance value is varies.
- Capacitance value is converted to voltage.
Usually MEMS microphone
is integrated with FET device.
MEMS Microphone Device Structure
Digital output of MEMS Microphone
-Amplifier and ADC in the same chip.
- Signal is modulated usually by PDM technique. (Pulse Density Modulation)
- Mono or Stereo option.
- Multiplexing option is available.
Human voice range : 300 and 3000 Hz
Voice Recognition Application
Bulk Micromachining MEMS Microphones
Surface Micromachining MEMS Microphone
Clean Si wafer.
Backplate deposition (Al), and paterning, etchant = 16:4:1 of (H3PO4), DI water, (HNO3).
Deposition Sacrificial layer (resist AZ1500).
Al diaphragm deposition.
Hole etching/acoustic paterning.
Etching sacrificial layer.
General microphone introduction
MEMS mic. overview
MEMS mic. structure and working principle
Fabrication of MEMS mic.
Digital output MEMS mic.
Application of MEMS mic.
June 20, 2013
Pulse Density Modulation