From shop windows, to phones, from fridges to bus-stops, displays are everywhere. And as their ubiquity increases, so we demand more from them. Indeed, some of the latest mobile phones offer graphical interfaces that ten years ago PC users could only dream about.
However, this unstinting demand for improved visual quality often sits uneasily with the equally pressing need for reduced size and lower power consumption. Hence, a headache for the designer.
This is why the zenithal bistable display (ZBD), an easy to manufacture development of the LCD which retains its image after the power supply is turned off, should have product designers rubbing their hands together with glee.
Inventor of the device, QinetiQ spin-off ZBD Displays Ltd, claims that ZBDs could dramatically reduce the amount of power required by portable electronic devices.Based on a single modification to the simple LCDs used in watches and calculators, the ZBD uses a simple microstructured surface to control the alignment of Liquid Crystal (LC) molecules.
These microstructured surfaces hold the LC molecules at the surface in either of two orientations.
Unlike conventional LCDs, the two LC orientations in ZBD displays are equally stable and switching from one state to the other occurs only after a voltage pulse of appropriate polarity.
This ‘bistability’ is not affected by thermal or mechanical effects, so that once an individual ZBD pixel is switched from ‘black’ to ‘white’, or vice versa, it remains in that state, even when the power is switched off.
By comparison, most conventional LCDs refresh images more than 30 times per second and require continual application of a voltage to each pixel to maintain either of these states.
ZBD claims that its displays offer enormous power savings, especially in applications with low image update rates, and will both extend the life of batteries and allow designers to substantially reduce the size and weight of their devices. The technology also enables high complexity displays with superior contrast, brightness and viewing angle without the additional expense of using thin film transistors (TFTs) behind each pixel, as used in laptop displays.
An extra advantage is the alleged ease with which ZBDs can be manufactured.Gratings are, claims ZBD, readily manufactured using simple photolithography and embossing techniques, and indeed, the company has already demonstrated prototypes with both glass and plastic substrates.
With wide manufacturing tolerances typical of a simple watch display, the technology is easily adaptable to existing passive matrix LCD production lines and is also ideal for plastic substrates (making roll-to-roll production feasible). It can be produced on TN glass, and uses standard STN drivers, liquid crystal materials, colour filter plates and device cell gap. Neither do ZBD displays need the additional expense of using thin film transistors (TFTs) behind every pixel, as used in laptop displays.
The company is still at the ‘discussion’ stage as far as applications go, but is confident that it won’t be long before ZBDs start appearing on commercial products. ‘The combination of zero power between image updates, unlimited image complexity and excellent readability, as well as suitability for flexible or standard plastic substrates, means that ZBD is placed at the heart of future portable electronic devices,’ says a spokesperson.
Mobile phones and PDAs are the obvious beneficiaries of the technology, but the company also anticipates its use in smart cards and electronic labels where it could be used to display data for extended periods without image degradation.
Indeed, ZBD claims that in tests, images have been stored for several years without degradation despite mechanical stress applied to the screen.