Capacitive Micromachined Ultrasonic Transducer (CMUT)

Capacitive Micromachined Ultrasonic Transducer (CMUT)

© Fraunhofer IPMS

Ultrasonic sensors are established for low-interference monitoring and analysis of static and dynamic processes in industrial testing and automation technology. Another field of application is medical diagnostics, where ultrasonic sensors are used.

Capacitive micromachined ultrasonic transducers (CMUT) are miniaturised sensor structures whose electrostatic operating principle enables the transmission and detection of ultrasonic waves. This new generation of ultrasonic transducers is manufactured using semiconductor technology processes and thus enables great flexibility in sensor design with high precision and reproducibility in the manufacturing process for single and multi-channel systems.

Features of the CMUTs at Fraunhofer IPMS:

  • wide range of elements with different frequencies (> 400 kHz)
  • high acoustic bandwidth (> 100% in immersion; > 20% in air)
  • high spatial resolution (submillimetre scale)
  • low acoustic losses
  • extreme miniaturisation (≤ 1 mm³). 

In addition, toxic substances (including lead) are not used in the  manufacturing process; the capacitive transducers of Fraunhofer IPMS are therefore RoHS-compliant.

The CMOS-compatible manufacturing process enables a new evolutionary stage in sensor miniaturisation due to the high integration potential with electrical control and evaluation electronics in CMOS technology. In addition, the natural acoustic matching to liquid and gaseous media ensures more efficient sound coupling. The extremely low mechanical coupling between individual sensor channels, in conjunction with the increased acoustic bandwidth, makes greater temporal and spatial resolution accessible. RoHS compliance ensures long-term usability.

Fraunhofer IPMS has many years of experience in the development of CMUT components and systems. A manufacturing process for CMUTs specially developed at Fraunhofer IPMS is used here, which enables CMUTs to be manufactured in the back-end-of-line (BeoL) process module. This allows the CMUT module to be integrated on standard CMOS processes, a unique selling point of this technology.

The amorphous metals used for the oscillating CMUT plates enable high long-term stability and reproducibility of the sensor elements. Within the clean room of Fraunhofer IPMS, highly integrated CMUTs can be developed on 200 mm wafers and manufactured in pilot series. Coupled with the competences in electronics development and ultrasonic signal processing, Fraunhofer IPMS offers the entire value chain for the research and development of CMUTs. This portfolio includes in particular services in consulting, development, characterisation and prototypical provision of CMUT components, CMUT modules and CMUT systems as well as pilot production.

Possible application scenarios for the single- and multi-channel CMUTs are distance sensor technology for collision monitoring and micropositioning, tactile sensor technology for force measurements and gripping processes, e.g. in robotics, acoustic spectroscopy (e.g. concentration measurement and ageing monitoring), flow analysis of liquids and gases (e.g. spirometry), ultrasound imaging (sonography, surface imaging) and photoacoustic applications.

CMUT applications

Application

Collaborative robot (CoBot) - safety through environmental sensing

Application

Spectral condition detection via ultrasound

Application

Tactile close distance sensing

Application

Ultrasound-based imaging for medical and measurement technology

Project

Modulable Acoustic Impedance through Metamaterials (MAIM)

Services

CMUT Evaluation Kit