Milestone-Proposal talk:Amorphous Silicon TFT Switches
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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. "
words for citation -- Tonydavies (talk) 11:11, 1 July 2017 (UTC)
I understand that the currently-recommended Citation for the proposal "Amorphous Silicon Thin Film Field-Effect Transistor Switches for Liquid Crystal Displays, 1979" is as follows:
A research team in the Physics department of Dundee University, led by Walter Spear and Peter LeComber, demonstrated in 1979 that amorphous silicon field-effect transistors were able to switch liquid crystal arrays. The invention enabled the development of the first generation of flat panel television displays.'
I have the following remarks about this Citation:
I wondered about the definition of '"first generation flat panel displays' - are there 'well defined generations' for these and if so what is the 'second generation' etc.? What 'generation' do we have now? I feel that the adjective 'large' ought to be there somewhere, because for very small displays, CRT technology could be used to make virtually flat displays.
For digital computers the use of 'generations' does have an approximate meaning, but I do not remember hearing it used in television - so for a citation intended for public display it does seem a bit questionable. Maybe what is really meant is just "..... enabled the development of the first [large] flat panel television displays"
Should we ask Cyril Hilsum for his opinion on the citation? Almost certainly he will not read this and almost certainly he will not be able to find the Milestone Proposal and read it in order to comment upon it, although he is surely the most knowlegeable living person who knows about the background details of this proposal.
Tony Davies, 1st July 2017
Removing proper names -- Allisonmarsh (talk) 20:53, 21 September 2017 (UTC)
Just a reminder that Milestones are supposed to be honoring an achievement, not individual people. Should we exclude the names of the research team leads? I'd suggest the following change:
In 1979 a research team in Dundee University's Physics Department demonstrated that amorphous silicon field-effect transistors were able to switch liquid crystal arrays. The invention enabled the development of the first generation of large flat panel television displays.
At 37 words, there is room to add more description/impact. I am not an expert in the field, any ideas?
Re: Removing proper names -- Jason.k.hui (talk) 14:35, 22 September 2017 (UTC)
Agree that names of people should not be in the Milestone citation unless it's absolutely critical. I think the citation is a bit short and needs another sentence. The advocate might want to circle back with the proposer and get something in before the History Committee telecon.
Re: Removing proper names -- M.j.bastiaans (talk) 13:41, 25 September 2017 (UTC)
In principle I agree, especially if we speak about names in the title of the Milestone. Using names in the citation is a bit less critical. In this particular case, I could allow the two names, because I feel that they are used/needed to identify which research group in the Physics Department did the work. 'A research group' by itself, as it is written now, may be too vague.
New version of the Citation -- Juan Carlos (talk) 17:50, 2 October 2017 (UTC)
Following the Committee's request, the proposers came up with a new, enhanced citation:
A research team in the Physics department of Dundee University, Scotland, directed by Walter Spear and Peter LeComber, demonstrated in 1979 that amorphous silicon field-effect transistors were able to switch liquid crystal arrays. Other semiconductor thin film materials had been found to be unsuitable for deposition on large area substrates. The invention laid the foundation for the commercial development of flat panel television displays
As the advocate, I find it much, much better than the original, and endorse it. The names of the researchers need also to be included in the citation. I think we could also sligthly adjust the second sentence, -which makes reference to materials only- and also highlight the significance of the whole deposition process, for instance as follows:
Previously, other procedures for obtaining thin film transistors had been found to be unsuitable for deposition on large areas.
- 1 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)
- 2 advocate approval -- Juan Carlos (talk) 16:46, 16 June 2017 (UTC)
- 3 words for citation -- Tonydavies (talk) 11:11, 1 July 2017 (UTC)
- 4 Removing proper names -- Allisonmarsh (talk) 20:53, 21 September 2017 (UTC)
- 5 New version of the Citation -- Juan Carlos (talk) 17:50, 2 October 2017 (UTC)