Qualcomm’s iMoD Display Technology

Biomemetics is the imitation of nature for a technological solution. Qualcomm have reverse engineered nature’s microscopic structures for producing the stunning colors of a butterfly’s wings. Nature’s technology is termed “interferometric” where colors are produced by causing light to interfere with itself.

Qualcomm recently presented on progress with their new Interferometric Modular Display (iMoD) technology to the inaugural Society for Information Display’s Mobile Display Conference. Naturally as butterfly wings do not have a backlight, Qualcomm’s iMoD display is a reflective one rather than emissive as with a CRT television. Like the micromirror DLP chips from Texas Instruments, iMoD is a micro-electro-mechanical system (MEMS).

Being a reflective display technology, iMoD solves one of the detractions of current mobile display technologies of being very difficult to read in high ambient light environments (eg. direct sunlight). “But what about when it’s dark?” one might ask – Qualcomm will simply use a front-lighting technology to light the display.

Qualcomm’s iMoD display technology has a range of useful characteristics but, the one Presentation Technology Review’s editor believes will set it apart from other reflective display technologies is its excellent response time which makes video playback possible. Data from Qualcomm indicates that the response time is even faster than current LCD technology. iMoD’s easy scalability combined with it’s compatibility with current flat panel manufacturing techniques makes larger flat panel displays a distinct future possibility.

Summary of key characteristics of iMoD display technology:

Low power consumption – compared to rival emissive technologies;
Always On – changing state takes the most energy so the display can be left on;
Excellent readability – a contrast ratio similar to a book;
Fast response time – fast response time suitable for video playback – an advantage over other reflective display technologies;
Slim form factor – no backlight delivers a thinner form factor (less weight also);
Scalable – the technology is scalable for larger screen sizes;
Compatible with current manufacturing techniques - iMoD displays can be made on existing flat-panel display assembly lines - using existing materials;
Wide viewing angle.

iMoD Commercialization

At present Qualcomm is working on commercializing an iMoD Bichrome 1.8 inch display (gold and black are available at present) with 128 x 160 resolution for integration into cell phones, handheld GPS devices and other mobile consumer electronics. However, they are also well advanced in development of 64 and 512 color displays.

iMoD Display Technology in More Detail

An iMoD element is a MEMS device composed of two conductive plates. The lower plate is a thin film stack on a glass substrate and the upper a reflective membrane separated by an air gap.

The iMoD element has two stable states: - with no applied voltage the plates are separated, and light is of the color the element is “tuned” to is reflected - when a voltage is applied, the upper plate collapses on the lower stopping light reflection and turning the element black. The tuning of an element to a color is simply a matter of adjusting the air gap between the two plates. At present iMoD element density is about 400 – 1,000 dpi.

The final element required for the success of iMoD is “element memory”. iMoD elements possess an electro-mechanical memory called hysteresis. Once the upper plate has been pulled down by the applied voltage, it requires less energy to hold it than was exerted in pulling it down. This bi-stability means and iMoD display needs very little power to function.

Robust Technology

A couple of factors point to iMoD displays being a robust technology:

the displays are manufactured from inorganic material unaffected by environment factors such as extreme temperatures, humidity, and ultra-violet radiation;
as no dyes or pigments used for color creation, the risk of dye/pigment degradation over time is eliminated.