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Organic fab opens for manufacture of printed optical sensors

Nanoident is a company founded in 2004 and based in Linz, Austria, where it has formally opened what it describes as the world's first manufacturing facility supporting high-volume commercial production of printed-semiconductor products. The facility will use the company's organic Semiconductor 2.0 Platform to produce printed optical sensors. The 2.0 Platform is Nanoident's label for its core technology, which spans EDA tools, expertise in polymer liquid, conductive and semiconducting materials, and production(printing) processes.

Privately owned, Nanoident has invested €12 million in its new facility, in which it currently has four printing stations that it has sourced from suppliers such as Fujifilm Dimatix (www.dimatix.com), giving the facility a theoretical capacity of printing 40,000m2 of substrate per year. This, as company founder and CTO Franz Padinger observes, is a tiny fraction of the cost needed to set up a silicon wafer fab; however, he sees printed electronics not as competitive with silicon technology but as a new field opening up new markets in new classes of products. The facility is already delivering sample quantities of sensor products, and CEO Klaus Schroeter anticipates that this will ramp up to production volumes within months.

The printing processes are primarily ink-jet-based, although the company can also use screen printing for some tasks that do not require the highest resolution. Jet printing deposits materials in layers typically 100 nm thick, that have lateral feature sizes and resolutions of the order of 20 microns. At present the company can print up to 5050 cm on rigid or fl exible substrates, in its class-100 clean room. Almost any component in conventional electronics has its equivalent in organic printed form, and where appropriate, Nanoident can mount silicon die on the substrate as a hybrid structure. Recently, other companies have focused attention on light-emitting structures such as OLEDs; Schroeter envisages that his company will build emissive devices for applications such as optical sensors featuring their own light source, but he "wouldn't go into displays - there are too many companies with deep pockets in that space already."

Much of the company's key expertise, Padinger says, lies in the detail of dealing with the materials. It buys conductive polymers and other compounds off-the-shelf from materials- science companies, but for every application it precisely engineers and blends a specific set of "inks" : they must give the desired electrical properties, and also must be correct in parameters such as viscosity so that they print correctly. The sequence of solvents must also be compatible so that later layers in the process do not dissolve those fi rst laid down.

The optical sensors have sensitivities"as good as if not betterthan" those achievablein silicon, and are linear oversix to seven orders of magnitude:a sensor pixel can be anysize from 2020 microns to5050 cm. Individual devicesare addressable in densearrays without requiring activetransistors at each sensor point.Nanoident can also "tune" photosensorresponse (by materialproperties, not by fi ltering) to befrequency-specifi c, to as closean accuracy as 10 nm inwavelength. Although the basicmechanism of charge generationand transport is differentfrom that of silicon, semiconductingbehaviour is very closelyanalogous. In the case of alight sensor, incoming photonsgenerate charge pairs that migratethrough the bulk material,resulting in a current at anexternal detector.

Devices that Nanoident currently builds do not require fast or high-gain active devices; if you want to build those, Schroeter says, you need two key things: materials with the right properties such as electron mobility - which the materialsscience suppliers are working on - and the ability to print submicron structures. Such technologies do exist, he says, "and we are exploring them" - adding,"ink-jet is only at the beginning[of its development] andis already capable of printingstructures down to a few micronsusing smaller drop sizesthan those employed today."

Nanoident has two subsidiaries in application-specifi c product areas. One, Nanoident Biometrics, focuses on printed semiconductor sensors - specifi cally fi ngerprint sensors. The company's optical technology can simultaneously image a fi ngerprint pattern, detect underlying skin structure and transcutaneously make haemoglobin/ bood-oxygen measurements. It is exploring markets such as the application of thin, low-cost sensors to mobile phones and other portables.

Bioident, the other subsidiary, makes disposable "lab-on-achip" sensors for medical diagnostics and other chemical tests. The underlying technology is - again - the printed organic light detector. A typical sensor will test for the presence of multiple compounds on multiple detection sites. Each sensitive point has an optical detector in close proximity to an"assay" - a compound that reactsto the chosen chemical targetby fl uorescing. The strengthof Nanoident's technology, saysBioident's CEO Wasiq Bokhari,is that the assay and detectorcan be in very close proximity,which greatly increases sensitivity.

Their minimum separation is only the thickness of the substrate, as little as 50 microns, ensuring effi cient capture of emitted photons. Printed on such thin substrates, the sensors can also be economically disposable. Beyond the medical sphere, Bioident is active in the security arena with sensors for "chemical- and biologicalthreat detection."

By defi nition, there is no need to seal the chemical sensors from atmospheric contaminants, a problem that has plagued other researchers in printed organic electronics - according to CEO Schroeter. Where long lifetimes are needed, the company can package devices in glass/glass or glass/metal structures and achieve lifetimes exceeding fi ve years. Some of the largearray industrial photosensors the company already makes are on thin fl exible substrates and have to achieve a required lifetime of around one month, which is achievable without sealing.

- by Graham Prophet

Nanoident, www.nanoident.com.