New-Tech Europe | Q2 2020 | Digital Edition

Technology platforms for MUTs Imec is developing technology platforms for MUTs, leveraging its long- term track record in developing micro- electromechanical systems (MEMS). In the past, the focus was on developing CMOS-compatible cMUT technologies. This has resulted in a high-performance cMUT technology platform. Today, imec is focusing on developing generic pMUT technologies that can be tuned towards haptic feedback applications. Two different platforms for pMUTs are being pursued: Si-CMOS- compatible and display-manufacturing- compatible technology platforms. Each of these platforms brings its own advantages and challenges. A Si-CMOS-compatible technology platform for pMUTs pMUTs can be post-processed directly on top of Si-CMOS. The main benefit of this approach is the ability to smoothly integrate the pMUT array with the driving and read-out electronics, either by wire-bonding or by using through-silicon vias – resulting in single-chip solutions. By using mature Si-CMOS-based processes in combination with Si- based pMUTs, highly integrated, efficient, high-resolution and high- performing pMUT arrays can be build. The footprint of the final pMUT chip is limited to typically 2x2cm2. Following this approach, imec develops with a foundry partner a generic Si-CMOS-compatible pMUT platform, with (scandium doped) aluminum nitride as the piezoelectric ‘vibrating’ material. As such, ultrasound waves are emitted in the 3-15MHz frequency range. To be useful for haptic feedback applications, imec and its foundry partner are tuning this generic

Figure 2: Dual thickness cMUT cells in an array.

Figure 3: Operation principle of cMUT and pMUT technology.

Towards a display- manufacturing- compatible technology platform for pMUTs Asecond family of pMUT technologies implements polymer-based pMUTs

platform towards lower frequencies, i.e. 200-600kHz – by using larger membranes (0.8-1.5mm diameter) with higher aspect ratio. The pMUT process can be adapted to specific use cases and is available for low- and high-volume production.

Figure 4: Microscopic picture of a pMUT array.

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