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Docket #:2017-15

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:


Title of the proposed milestone:

Silicon Controlled Rectifier (SCR/Thyristor), 1957

Plaque citation summarizing the achievement and its significance:

General Electric introduced the silicon controlled rectifier (SCR), a three-terminal p-n-p-n device, in 1957. The gas-filled tubes used previously were difficult to operate and unreliable. The symmetrical alternating current switch (TRIAC), the gate turn-off thyristor (GTO), and the large integrated gate-commutated thyristor (IGCT) evolved from the SCR. Its development revolutionized efficient control of electric energy and electrical machines.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

In what IEEE section(s) does it reside?

Rochester, New York

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

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

Unit: Power Electronics Society
Senior Officer Name: Alan Mantooth, President

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: Power Electronics Society
Senior Officer Name: Alan Mantooth, President

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

IEEE Section: Rochester, New York
IEEE Section Chair name: Sreeram Dhurjaty

Milestone proposer(s):

Proposer name: W.G. Hurley
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 in decimal form of the intended milestone plaque site(s):

124 Columbia St, Clyde, NY 14433, USA

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. The site at Clyde NY is the location of the original invention. It is the headquarters of Advanced Atomization Technologies, which in turn is a joint venture between GE (the inventors of the SCR/Thyristor) and ParkerAerospace

Are the original buildings extant?


Details of the plaque mounting:

Location near the entrance, on the outside of the building, at eye level and fully visible to the public.

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

Fully visible and accessible to the public.

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

The Advanced Atomization Technologies, A Parker Aerospace & GE Joint Venture, Clyde New York

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

The invention of the SCR/Thyristor revolutionized the control of electric power conversion by replacing the gas-filled controlled rectifier tube (the thyratron) with a three-terminal solid-state device consistiing of an anode, a cathode and a gate. Unlike the two terminal diode in which current flows when a positive voltage is applied between the anode and the cathode, the SCR will not conduct with a positive anode-cathode voltage until a small voltage is applied between the gate and the cathode. Conduction is stopped by reducing the current to a low value known as the latching current.

The invention of the SCR/Thyristor led to dramatic efficiency and control improvements in the rectification of line voltages and is the basis of modern speed control of ac and dc motors. Its application to motor control had a substantial impact in electric traction, making possible the displacement of dc motors by the more efficient and reliaable ac motors, particlulaly in railroads. The SCR and its derivative, the GTO, have made possible HVDC transmission at much higher voltages and power levels than previously obtainable with mercury arc rectifiers and thyratrons.

The SCR has also had a dramatic impact on manufacturing.The steel, electrochemical, automotive and welding industries, among many others, benefited greaatly by the improved efficiency, more precise control, and reduced cost made possible by the application of SCR based equipment to their processes.

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

The functional basis of the SCR as an interconnection of two transistors was originally described as early as 1950 and published by J. J. Ebers of Bell Laboratories in 1952. The subsequent reduction to practice as a monolithic device required a deeper understanding of the current dependency of the current gains of the two transistors, and recognition that silicon and not germanium was the appropriate semiconductor to use. Problems of false triggering by thermally or dv/dt induced currents at the triggering junction also needed to be understood and solved. Initial devices demonstrated relatively low power ratings, leading some to believe that the SCR was not destined for high power applications. Improvements in silicon crystal growth and wafer processing lead to ever larger devices with ratings now exceeding 10 kV and 3 kA. Package design was another challenge as device ratings, and hence device dissipation, increased. The single-sided cooled, stud mounted device was replaced by the two-sided cooled “hockey puck” package in which the silicon was not bonded, but contacted by compression of the package thus allowing movement to accommodate thermally induced stresses in the large Si wafer. A further obstacle to extending the application of the SCR is the speed at which it is capable of switching. Early devices could be applied at frequencies not much higher than 10’s of Hz. A better understanding of device behavior and Improvements in device design and fabrication have produced devices capable of operating at frequencies in the 10’s of kHz.

What features set this work apart from similar achievements?

Among similar achievements are the thyratron, the bipolar transistor (BJT) and the field effect transistor (FET), devices which were invented before the SCR. The SCR made the thyratron obsolete by manifesting it’s function in a smaller, more efficient, more reliable and more easily controlled solid state device. In addition, the SCR can exhibit power ratings far exceeding the thyratron’s. Besides its ability to control much higher power levels, the singular feature of the SCR that sets it apart from the BJT and FET is its bipolar voltage blocking capability. The BJT can support a voltage of only one polarity and thus cannot function in applications for which the SCR is appropriate. Due to materials issues the FET had a long gestation period before it became a practical device, and it wasn’t until the 1970’s that the vertical channel power MOSFET was developed. Like the BJT, the FET is incapable of bilateral voltage blocking and cannot be used in place of the SCR.

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.

[1] E. L. Owen, "SCR Is 50 Years Old", IEEE Industry Applications Magazine, Volume 13, Issue 6, Pages 6 - 10, 2007

[2] N. Holonyak, "The Silicon p-n-p-n Switch and Controlled Rectifier (Thyristor)",IEEE Transactions on Power Electronics, Volume 16, Issue 1, Pages 8 - 16, 2001

[3] Deepak Tiku,, "dc Power Transmission: Mercury-Arc to Thyristor HVdc Valves", IEEE Power and Energy Magazine, Volume 12, Issue: 2 Pages: 76 - 96, 2014

[4] M. Korytowski, "Uno Lamm the father of HVdc transmission", IEEE Power and Energy Magazine, Volume 15, Issue:3 Pages: 92-102, 2017

[5] GE SCR Manual, 5th Ed., GE Syracuse New York, 1972

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 Please see the Milestone Program Guidelines for more information.

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 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).

Please recommend reviewers by emailing their names and email addresses to Please include the docket number and brief title of your proposal in the subject line of all emails.