Milestone-Proposal talk:Amorphous Silicon TFT Switches

Revision as of 17:29, 16 June 2017 by Juan Carlos (talk | contribs) (advocate approval -- Juan Carlos (talk) 16:46, 16 June 2017 (UTC))

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This proposal would benefit from links (or texts that are accessible without having need for access to XPlore) -- Microman (talk) 07:52, 25 April 2017 (UTC)

1. Peter LeComber and Walter Spear in 1979 conducted the first successful experiments that demonstrated the feasibility of using thin films of amorphous silicon in large area flat panel displays. It is cited in references a, b, c, and d as the most significant advance in flat panel technology. 2. Paul Weimer had reported in 1962 that it was possible to produce transistor action in thin film field effect devices. His paper announced the arrival of this new type of transistor which eventually became the preferred choice of switching device for flat panel displays. 3. Peter Brody and his team at Westinghouse Research reported their work on a ‘state of the art’ liquid crystal display that demonstrated that, in principle, practical-size substrates could be employed using directly addressed discrete thin film silicon transistors. 4. Howard’s 1992 paper reviews the progress achieved with thin-film transistor/liquid crystal displays. He cites the work of LeComber and Spear with the comment that ‘the report of an amorphous silicon TFT by LeComber et al in 1979 must be considered a major milestone’. 5. The paper by Hilsum in 2016 points out that the use of amorphous silicon by LeComber and Spear was entirely novel and unexpected, and followed a long sequence of unsuccessful attempts by other groups to use deposited films of other materials for fabticating the switching matrix. 6. The paper by Depp and Howard in 1993 notes that the advantage of the approach adopted by LeComber and Spear was that was cheaper than the alternatives, and therefore more commercially viable, and that the processing was simpler. 7. The review paper by Kuo in 2013 also cites the LeComber and Spear work as providing ‘the breakthrough in the field’.

advocate approval -- Juan Carlos (talk) 16:46, 16 June 2017 (UTC)

The proposal is about work done by investigators at the Univ. of Dundee, demonstrating in 1979 a process to build Thin Film Transistors (TFT) on a hydrogenated Amorphous Silicon  (a-Si:H ) substrate, Each of those transistors was capable of driving a pixel of a Liquid Crystal Display (LCD). It is documented and recognized in the Literature presented.

However and not being an expert in the field, some doubts arised about the real significance, the transcendence of this work. Was it really was a turning-point deserving an IEEE Milestone or just another step in the long way from Liquid Crystals to the modern display technology?

The original concept of a matrix Liquid Crystal Display originated in RCA in the 60's (there is an IEEE Milestone for that). In 1973 Peter Brody demonstrated a 120x120 pixels display, for which an an IEEE Award was given: IEEE Jun-Ichi Nishizawza medal  2011 "For pioneering contributions to thin-film transistor  (TFT) liquid-crystal displays. " In 1988 Sharp demonstrated a 14" TV display (another approved IEEE Milestone)

An independent opinion was sought. The Electronic Devices Society and the Solid State Circuits Society were contacted, asking for Experts, and after some unsuccessful intents, we finally got a very conclusive, positive and substantiated answer from a recognized expert in the field. It's particularly valid because he has been doing related work at PARC from that time.

As the advocate, I'm approving this Milestone Proposal and recommending to the Committee for Approval. We are working with the Nominator to finish the Citation.


From Dr Robert Street, Senior Research Fellow at Palo Alto Research Center ( 2010 AIP Industrial Physics Prize "For pioneering contributions to the science and technology of hydrogenated amorphous silicon, and the development of flat panel x-ray medical imaging )

" In my opinion, the Dundee TFT is appropriate for an IEEE Milestone. As you point out, the concept for an active matrix LC display predates the Dundee work, as does the development of CdSe semiconductor TFTs by Brody, and the Dundee group was familiar with this prior work.  However, the CdSe TFTs were difficult to make and efforts to develop them into a full technology did not succeed. Perhaps eventually this technology would have worked but the a-Si:H TFT developed by Spear proved to be so much better and easier to make with uniformity and reliability that rapid development followed and led to the present huge flat panel display industry.

" The success of the a-Si TFT depends on some key features which the Spear lab largely developed by itself.  First is the high quality of the a-Si material itself.  The PECVD growth method was developed by Stirling several years earlier but picked up by Spear who did the main work of showing that it has high carrier mobility and low defect density, both of which are pre-requisites for the TFT.  Second, Spear showed that it was possible to dope a-Si n- or p-type which provides an ohmic source and drain contact that is essential for a good TFT, but which was difficult to achieve in the CdSe thin films. Third was the PECVD SiN gate dielectric that proved to have high performance, and was also largely developed by Spear’s group.  The fact that the gate dielectric, the semiconductor layer and the doped contacts were all made by PECVD and could be done in the same deposition reactor was an important factor in the performance because oxidation or other surface contamination arising from removing the film from the vacuum system could be avoided.


"The TFT described in the 79 paper has the bottom gate structure and a PECVD fabrication process that is identical to the TFTs in current use.  Hence, Spear developed all the elements – materials, device structure and fabrication process – that is in the current technology, essentially without change. "