Milestone-Proposal:Amorphous Silicon TFT Switches


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Docket #:2016-07

This Proposal has been approved, and is now a Milestone


To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes


Year or range of years in which the achievement occurred:

!972 - 1980

Title of the proposed milestone:

Amorphous Silicon Thin Film Field-Effect Transistor Switches for Liquid Crystal Displays, 1979

Plaque citation summarizing the achievement and its significance:

A research team in the Physics department of Dundee University, Scotland 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.

In what IEEE section(s) does it reside?

United Kingdom and ireland

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: United Kingdom and ireland Section
Senior Officer Name: Dr Ali Hessami

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: United Kingdom and Ireland Section
Senior Officer Name: Dr Ali Hessami

IEEE section(s) monitoring the plaque(s):

IEEE Section:
IEEE Section Chair name: {{{Section chair name}}}

Milestone proposer(s):

Proposer name: Charles W Turner
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates of the intended milestone plaque site(s):

Physics Department, Dundee University, Dundee, Scotland, UK

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. University department building.

Are the original buildings extant?

Yes

Details of the plaque mounting:

The plaque will be mounted on the outside wall of the building.

How is the site protected/secured, and in what ways is it accessible to the public?

The plaque will be bolted to the outside wall of the building and will be readily visible to visitors to the Dundee University campus.

Who is the present owner of the site(s)?

Dundee University

What is the historical significance of the work (its technological, scientific, or social importance)?

The cathode ray tube (CRT) provided the principal means for displaying dynamic images from the 1930s until the advent of liquid crystal displays in the 1960s and 1970s. The standard level of definition for practical devices suitable for high data rate applications such as television, required that millions of pixels needed to be addressed for each frame to be displayed. This presented no special problem for electron beams scanned across a phosphor screen, but in a flat liquid crystal display direct electrical connection to each element was an essential requirement. At the selected pixel a switching voltage had to be supplied to turn on the local zone of the liquid crystal film for a very short time interval. This action allowed the back-lit light source to be viewed by the observer in front of the display. The complexity of connecting such a large and compact array of elements required a wiring matrix on a microscopic scale that could only be achieved by using a conducting film from which the circuitry could be fabricated. By using the film in the form of an amorphous silicon layer Spear and LeComber were able to design a series of switching transistors able to perform the necessary switching function at each pixel. Their breakthrough pointed the way for the manufacture of large flat panel displays.

What obstacles (technical, political, geographic) needed to be overcome?

The biggest challenge in the way of achieving progress was the lack of available semiconducting materials with the right properties to allow switching devices to be integrated into the backplane of the display. Thin film transistors (TFTs) had been fabricated earlier using deposited semiconductors but none was suitable for a commercial device. It was accepted that deposited films of semiconductor materials were generally of poor quality, compared with single crystal materials. The group at Dundee adapted the method used by Stirling, in which hydrogen was added to amorphous silicon, producing a-Si:H, allowing n-type and p-type doping to be possible. Transistors manufactured in 1978 using the a-Si:H material showed great promise as switching devices. The Dundee group demonstrated in 1979 that a TFT array for LCDs was feasible. The most important advance over the previous attempts by the RCA group was that a stable semiconducting layer had been developed.

What features set this work apart from similar achievements?

The concept of incorporating a switching device at each pixel of a flat panel display was first proposed by the RCA group of Weimer in 1961. It was not until a material able to be deposited over a large area suitable for a flat panel display became available that the invention could be used in a practical device. The semiconducting properties of thin layers or films are quite different from those of single crystal or polycrystalline versions. For example, conventional devices such as bipolar or field-effect transistors made from such films have generally poor performance. The Dundee group discovered that TFTs made from films of amorphous silicon to which hydrogen had been added (a-Si:H) could be used as effective switching devices.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

The most significant references are provided with this submission, and are on file with the staff of the IEEE History Center.

The following references have been chosen in support of the Milestone application for the recognition of the work of the Dundee University, Scotland, to develop amorphous silicon switches for flat panel displays.
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’.

In summary, these references confirm that the progress achieved since the 1960s towards a flat panel display using liquid crystals was punctuated with many disappointments. The lack of success in trying to use conventional semiconductor technology continued until the Dundee University group showed that amorphous silicon offered a better solution.

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.

Supporting materials are provided with this submission. Because of copyright, they may not be posted here. However, copies are on file with the staff of the IEEE History Center.

Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to ieee-history@ieee.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).