New-Tech Europe | Q2 2020 | Digital Edition

that are fabricated in a display- ma n u f a c t u r i n g - c omp a t i b l e , large area technology. The true advantage of this technology is the ability to beam ultrasound waves from a large area array (in the order of a few to several tens cm2), resulting in a potentially larger power output and a fine non-contact haptic experience. This could be used for creating mid-air haptic feedback sensations from a greater distance, e.g. to enable interactive posters for enhanced digital advertising. Applications can go beyond display-based integrations – think about mid-air haptic feedback experiences generated from the windows of your house. This technology is currently under development, and first proof of concepts have emerged. At imec, for example, a 4cm x4cm large 64x64 array of 480µm diameter pMUTs were fabricated. The 64 by 64 array consists of four 32 by 32 arrays. First generation devices are made with a piezoelectric polymer, while the next generations under investigation will use piezoelectric ceramics. Imec ultimately aims at integrating these pMUT arrays with thin- film transistor backplanes (as the driving electronics) and fabricating them in unprecedented array sizes in display-manufacturing- compatible technology platforms. An attractive approach is to install these MUT capabilities in display fabs that have recently shifted to newer display technologies and make their older capacity available to more diverse products. This is very comparable to the experience in CMOS where capacity became available in 200mm facilities that were re-used for MEMS development and eventually for MUT development.

Figure 5: 64x64 array of polymer-based pMUTs.

The broad potential of MUTs: from haptic feedback to brain stimulation First commercial haptic feedback products have already entered the market, mainly in the form of plug-and-play modules that allow to enrich the interface of existing entertainment installations with virtual buttons or magical sensations. These applications typically implement bulky classical ultrasound transducers, limiting the ultrasound frequency (to typically 40kHz) and as such the haptic feedback experience. As alreadymentioned,micromachined ultrasound transducers are expected to open entirely new avenues, by enabling compact and portable solutions with finer sense of touch. In this implementation, haptic feedback will enhance remote control of machines and create advanced

human-machine interfaces for automotive or advanced displays. For example, it can be used to enlarge the small touch screen of your smart watch into a full hand interface, or to enhance interactive digital advertising through large ‘haptic’ posters. It may also become a key part of virtual reality/augmented reality systems, adding sense of touch to previously visual-only interfaces. It will enable touch from a far distance, like a virtual handshake. Or, in medicine, it can be of great value for remote surgery, making the surgeon feel what he remotely touches – assisted by gesture recognition. But the potential of micromachined ultrasound goes beyond haptic feedback. First, the ability to beam ultrasound energy to one focal point is being explored in medicine, for neuromodulation, brain surgery or cancer treatments. Ultrasound transducers can also be used to generate direct sound: tightly

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