/ Inscription
Mon espace

Printed Thin Film Transistors to be discussed in Tokyo

BE - Entreprises & initiatives

A diverse toolkit of electronic components can today be printed. These include batteries, antennas, memories, sensors, etc. An important building block linking all these components is the printed thin film transistor. This vital device enables logic and therefore data processing. Despite years of development however, printed transistors are not yet a commercial reality. 

Far Asia is the primary centre for the development and production of thin film transistors, which are used in display, X-ray detectors, large-area photosensors, etc. Global companies like Samsung and LG are leading the way. This has promoted us to dedicate a session to “Printed Logic” in our Printed Electronics Asia event,,  which takes place October 2-3, 2012 in Tokyo.

In this short article, we will give a brief overall assessment of printed electronics, outlining critical challenges facing printed transistors from both a market and technical prospective. This article will help set the parameters for the debate that we hope to promote in our event.

Where is the value in printing transistors?

Today, we have a rapidly increasing range of material options available for fabricating TFTs, including oxides, organics, etc. In spite of this, amorphous and polycrystalline silicon remain the dominant technologies.

The current fabrication method are all subtractive, regardless of the specifics of the deposition or annealing technique (e.g., plasma enhanced chemical vapour deposition, sputtering, excimer laser annealing, etc).  This is because a photolithographic patterning technique can require more than six steps for deposing a single layer. In addition, much of the deposited material is etched away and thus wasted. This adds to both the bill of materials and the processing cost.

In contrast, printing techniques offer an additive fabrication technique. Here, a layer can be directly deposited with as little as three steps. More critically, material wastage will be minimised. These two factors indicate a potential cost saving. It is this strong rationale that underpins the drive towards printed thin film transistors.

Printing thin film transistors offer numerous other advantages too. Primary amongst them are the ability (a) to cover large areas and (b) to print on low-temperature flexible substrates such as paper. Both these attributes can enable a broad range of new markets including ultra large sensor arrays, smart packaging and point-of-sale posters, etc.

What are the challenges?

The technology is at a state where we have a range of printable semiconductor (e.g., the active channel in the transistor) at our disposal. This toolkit includes organics, oxides, CdSe, crushed silicon, liquid silicon, carbon nanotubes, nanowires, etc. None of this semiconductors offer a one-size-fits-all solution and all suffer from significant limitations, including:

Low mobility: field-effect mobility is a key figure-of-merit which determines how fast transistors can switch. Printable semiconductors typically struggle to reach the 0.5-1 cm2/Vs mark. Even reaching this value will not sufficient for many emerging applications, including OLEDs. Indeed, it may not be sufficient to displace the current incumbent technologies, such as amorphous and polycrystalline silicon, which offer 1 and >100 cm2/Vs, respectively.

Low stability:  thin film transistors are interfacial devices. A poor interfacial quality (e.g., high density of defect states) will result in unstable devices whose characteristics change during operation. In addition to this, the absence of ultra-high-performance encapsulation can lead to device degradation, particularly when organic semiconductors are involved. This is a major handicap because circuits are designed to tolerate a range of characteristic variations and will cease to function once the device drifts out of the compliance range. Increasing the compliance range will significantly drive the costs up as it often requires incorporating more transistors.

Low spatial uniformity: device characteristics must remain uniform across the device surface in order to maintain a uniform brightness distribution. Therefore, the manufacturing technique must be able to reproduce the same conditions (geometry, contact, interface, etc) over large areas. This is proving to be a major challenge with printing equipment.

Dielectrics: research has been mainly focused on printed semiconductors. This, however, is only a part of the picture. We will also require reliable, pin-hole-free printable dielectrics. This is a challenge, particularly because the annealing and wetting properties of the ink must be compatible with both the under- and over-lying layers. In addition, the printed dielectric must withstand subsequent processing conditions. The outstanding questions over printed dielectrics are likely to mean that printed transistors will initially consist of hybrid structure in which only the semiconductor and the conductors are printed.

Low temperature annealing: flexible substrates tend to have a low annealing temperature. They will constrain the device processing conditions. In turn, this constrain will lead to poor device performance because often high-temperature annealing is a prerequisite for high-quality devices.

In addition to technical challenges, printed thin film transistors are actively searching for markets.  In many application areas, the main go-to-market strategy is replacing an existing component/layer in a product. This is a challenge because the incumbent technology is often well-entrenched.  Two primary high-volume target markets for printed transistors are:

RFID tags: here the printed versions are envisioned to replace crystalline silicon chips. The challenges however are the HF and UHF communication protocol require the integration of thousands of transistors running at 13.56 MHz and 865-960 MHz, respectively. Given the lack of uniformity, reproducibility and mobility, we assess that displacing silicon will be very difficult. In addition, printed chips will occupy more space. Finally, the RFID business is a pure cost game in which margins are very small (<1 cent) and huge volumes are required for reasonable profits.

Displays: printed thin film transistors may lower the production cost for display backplanes. The challenge here will be lifetime (i.e., change of characteristics during operation) and uniformity. Mobility will also be critical when moving towards OLED and/or 3D display. It is not clear whether printed thin film transistors can meet the technical requirements.

Lire la suite...

Articles en relation

BE - Entreprises & initiatives
Esteval Infos - 8 février 2019

Au sommaire de nos publications cette semaine, 58 articles (accès libre et accès abonnés) dont : Lancement du fonds Candriam Equities L Oncology Impact Dette émergente : une classe d'actifs attrayante pour 2019 Comme chaque mois, retrouvez nos sélections de produits d'investissement : Notre liste de fonds de boutiques revient en territoire positif Notre liste diversifiée rebondit de 2,3 % sur un mois       Une fin d'année 2018 solide pour le marché locatif des bureaux...

ER - Patrimoine et placements
[Les entretiens d'Esteval] Jean-Claude Chasson, Bacchus Conseil

Bacchus Conseil : Une vision durable et raisonnable de l'investissement « plaisir » Loin des spéculations observées ces dernières années sur les bouteilles de vin, Monsieur Jean-Claude CHASSON s'est spécialisé avec Bacchus Conseil dans le développement durable et harmonieux du patrimoine viticole français. Retour sur une belle aventure entrepreneuriale avec le fondateur de l'entreprise. Quand avez-vous créé votre premier GFV ? C'était en 1989. Dans le cadre de l'expertise comptable et fort de...

BE - Entreprises & initiatives
Nominations professionnels du droit

Bernard Cendrier, Senior Advisor opérationnel chez Deloitte Corporate Finance Il apporte à l'équipe animée par Charles Bédier son expertise et sa connaissance, notamment des secteurs de la chimie, du facility management et de l'énergie. Fort d'une expérience de plus de 30 ans, Bernard Cendrier a occupé différentes fonctions de direction chez Gaz de France, Estampille SA, Engie, Desk Finance M&A et Rhodia. En 2008, après la reprise de Rhodia par Solvay, il devient Directeur des Fusions &...

BE - Entreprises & initiatives
Affacturage : Factofrance accompagne ses clients aux Etats-Unis

Complémentaire à un contrat d'affacturage français ou Paneuropéen, cette offre proposée par Factofrance, acteur dans le secteur de l'affacturage en France, permet aux entreprises éligibles de financer le développement de leurs filiales américaines Les Etats-Unis est un pays d'implantation privilégié des entreprises françaises, où ces dernières réalisent 16% de leur chiffre d'affaires, soit 203 Mds€. Viennent ensuite l'Allemagne avec 117 Mds€ et le Royaume-Uni avec 108 Mds€. Les Etats-Unis...