Lateral Micromechanical Ultrasonic Transducer (L-CMUT)


© Fraunhofer IPMS
L-CMUT glued on printed circuit board with wirebonds & bondlands.

Among sensors, ultrasonic transducers are the all-rounders that have established themselves for many detection tasks in technical applications. The use of sensor systems for the exchange of information in the near-distance and contact range is becoming increasingly important. For example, in gesture recognition or collision warning. The application area of gesture recognition in particular increasingly requires miniaturised sensors with low energy consumption in order to integrate them into mobile internet-enabled end devices.

The novel ultrasonic transducers in MEMS technology, which were developed in the business unit Monolithically Integrated Actuator and Sensor Systems of Fraunhofer IPMS, can close this gap. The technology makes it possible to dispense with the membrane used in conventional ultrasonic transducers. Instead, microscopically small bending bars are used, which are set into vibration by a signal and oscillate in the chip plane. In order to generate sound, these bending beams are arranged in sound chambers and the sound exits the sound chambers via inlet and outlet slits.

Advantages of MEMS ultrasonic transducers

  • Volume utilisation → by utilising the chip volume, transducers with very small dimensions can be realised.
  • Low control voltages → control voltages of less than 48 V enable the use of the transducers in compliance with the low-voltage directive.
  • All-silicon → reliable CMOS-compatible manufacturing processes enable production in almost any clean room. Similarly, the transducers comply with the RoHS directive.
  • Frequency range → the frequency of a transducer can be finished in a wide range specific to the application. Frequencies from 20 kHz to 500 kHz are possible. Frequencies are adjustable within a range
  • Combination → sensor and actuator elements can be integrated directly adjacent in one component. In particular, this can also be implemented for different frequencies.
  • Flexibility → the transducers can be adapted to customer requirements in many ways. This includes the form factor, the radiation characteristic and the frequency range.

Application areas and status of MEMS ultrasonic transducers

The silicon-based ultrasonic transducers can be used in a wide range of technical applications. Examples are distance measurement, gesture recognition and non-destructive material testing for predictive maintanance.

MEMS ultrasonic transducers can be manufactured entirely in silicon. The proof of suitability as ultrasonic transducers was carried out with internal research projects and resulted in a demonstrator. The demonstrator evaluates the propagation time of a radiated and reflected signal, which makes it possible to recognise different gestures and distances.