Display Technology
The growing potential for MOEMS deployment
When most of us think of optically-oriented semiconductor components, it is probably in the form of LEDs made from gallium arsenide (GaAs) or gallium nitride (GaN), or perhaps CMOS-based image sensors. However, the value of micro electro-mechanical system (MEMS) devices in certain applications is becoming ever more evident. Innovations made by the leading manufacturers in this field mean that the age of micro- opto electro-mechanical system (MOEMS) technology is clearly upon us. Mark Patrick, Mouser, talks about how its growing potential
Mark Patrick T
he telecom and data centre sectors have brought about demand for micro-machined solutions (that integrate CMOS signal processing elements) to take care of switching and
control tasks. A technique that gained traction in telecoms industry from an early stage was precision alignment of optical fibres for interconnection purposes, via ferrules or V-shaped grooves etched upon the surface of a silicon substrate. Through precision etching the use of selective interference is also made possible – thereby enabling the filtering out and separating of channels in wavelength division multiplexing (WDM) systems. Such filters need not have a fixed frequency – thanks to the electro-mechanical properties of silicon micro-assemblies they can be tuneable. Displacements in the order of tens of nanometres prove sufficient enough to tune a filter to the wavelengths needed for effective fibre optic communications. Typically, the filter grating is split into respective fixed and moving parts. The moving part will have a cantilever structure, and is moved electrostatically as charge in the circuitry located just below it is raised and lowered accordingly. Larger scale cantilevers have been incorporated into optical switch devices, in which mirrors are positioned to reflect light emanating from a source channel into the allocated receiver channels.
Bringing heightened
sophistication to MOEMS, the digital light projector (DLP) products developed by Texas Instruments (TI) have gained a great deal of popularity over the course of the last decade or so. Each comprises a multitude of micro-machined mirrors (that measure less than one-fifth of the diameter of a human hair), organised into a Cartesian grid configuration. Once again relying on a cantilever
mechanism, every one of these mirrors can be caused to swivel through electrostatic attraction
18 September 2018 Components in Electronics
and repulsion. By adjusting the angle of the mirror in one direction, a light source can be reflected onto a particular x-y position on the target surface, while taking it in the other direction will mean that the light is reflected onto an
absorbing surface instead of the target – this effectively turns the ‘pixel’ that the mirror represents off at that time. To render different degrees of brightness, the mirror can be rapidly switched from one state to the
An electron microscope image of the micro-machined mirrors at the heart of TI’s DLP technology
other – with the ratio of on-time compared with off-time determining the shade produced.
DLP has played an integral part in bringing about the digital delivery of movies in cinemas and is the basis of the projection TVs now becoming more commonplace in our homes. Its scope within the domestic environment doesn’t stop there though. By utilising DLP technology, active displays can also be built into home automation equipment lacking the necessary surface area for conventional display arrangements. Through the use of ultra-short-throw projection optics the control panels associated with a security system or thermostat, for instance (which normally have quite limited room available for user interaction), are able to benefit from any wall space close by to act as a human-machine interface. An accompanying camera along with suitable gesture recognition software will be able to interpret the user’s hand movements and activate the desired control functions. The access to a more advanced form of human-machine interface thus derived means that much better user experiences can be provided.
DLP-based systems are able to make users aware when issues arise. For example, when a home security alarm is being set, the display can show the current status of all the doors and windows, warning the user if one of them has been left open. If a DLP is mounted above a kitchen work surface it can be of assistance during food preparation. Recipes and cooking instructions can be displayed in front of the user so that they have the information they need – delivered in a highly convenient way that doesn’t distract them from the job (as opposed to having to keep referring back to the cookery book – which is placed further away from the actual preparation area, so that it can be
kept clean). Dishwasher
and washing machines can display details of their operational status directly onto the floor. The control panels of these appliances thereby don’t have to incorporate displays that will spoil the aesthetics of the kitchen units. A simple gesture (such as a wave of the hand) close to the unit can be sensed by a camera or IR proximity sensor, so that the projection can be turned on or off.
In addition, DLP technology can be employed within 3D printing machines, with devices steering the lasers involved in formation of the required objects. There are also a host of new possibilities in a virtual reality (VR) context, where they can deliver the high-resolution, low-latency imagery needed by headsets, as well as playing a similar role in automotive head- up display units (HUDs). To address the applications that are starting to open up for DLP technology, TI now offers devices featuring resolutions going all the way from 640x360 for simple human-machine interface implementations right through to 1920x1080 for high-end smart home applications. Many of these devices support algorithms like IntelliBright, which can automatically adapt brightness, contrast and other parameters to suit different ambient lighting conditions and projection surfaces. MOEMS may still only represent a
relatively small proportion of the overall optoelectronics market, but the usefulness it exhibits in relation to the manipulation of light is becoming increasingly apparent. Home automation is already beginning to reap the rewards of including this technology. There are certain to be other opportunities in wearables, healthcare and various aspects of the Internet of Things (IoT) that will emerge in the coming years.
www.mouser.co.uk www.cieonline.co.uk
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