MEMS and sensors

Which MEMS-fabricated ultrasonic elements are sometimes used in under-display fingerprint sensors in smartphones and in medical ultrasound?

  1. AVCSELs
  2. BCCDs
  3. CPMUTs and CMUTs (micromachined ultrasonic transducers)
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Answer: C. PMUTs and CMUTs (micromachined ultrasonic transducers)

PMUTs (piezoelectric) and CMUTs (capacitive) are ultrasonic transmit/receive elements made with MEMS technology. They vibrate a thin membrane to emit ultrasound and detect the reflected waves. Because many elements can be arrayed in a semiconductor process, they are used to read fingerprint ridges and acquire ultrasound images.

  • A. A VCSEL is a vertical-cavity surface-emitting laser.
  • B. A CCD is an image sensor that detects light.
  • C. Correct. They are MEMS-fabricated ultrasonic transducers.
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More MEMS and sensors questions

  1. In surface micromachining, what problem occurs if a structural thin film such as polysilicon has large internal residual stress?
  2. In a MEMS electrostatic actuator, if the voltage between two parallel electrodes is doubled, by roughly what factor does the electrostatic attraction between them change? (Assume the gap is unchanged.)
  3. When choosing the measurement range of a MEMS accelerometer (for example, ±2 g versus ±16 g), which reasoning is correct?
  4. In a parallel-plate electrostatic actuator, what is the phenomenon called in which, as the voltage rises, the movable electrode suddenly snaps to the fixed electrode once it passes a certain position?
  5. Which method is widely used to evaluate the bias stability (slow drift of the output) of MEMS gyroscopes?