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Keywords:

  • amorphous semiconductors;
  • chalcogenides;
  • Stanford R. Ovshinsky

Abstract

  1. Top of page
  2. Abstract
  3. 1 The legend and the personality of a self-taught genius inventor
  4. 2 Working in ECD during my sabbaticals

Stan Ovshinsky, the man who practically started the field of amorphous semiconductors in the West, is 90 years old this year. He always keeps the enthusiasm of a teenager and the slim and tall figure of a cypress tree. Stan's personality actually reminds me of these characteristic trees of the Mediterranean landscape; with their narrow tall figures pointing towards the sky and popping out of any green background surrounding them. Stan feels and behaves as a young man; even at the age of 85, following his old dream for changing the world, he founded a new company. I first met Stan and Iris in 1977. Since then, I have spent several sabbatical leaves in Energy Conversion Devices (ECD), from 1984 to 2004. In the following, our scientific collaboration and the build up of a very deep and sincere friendship will be described.


1 The legend and the personality of a self-taught genius inventor

  1. Top of page
  2. Abstract
  3. 1 The legend and the personality of a self-taught genius inventor
  4. 2 Working in ECD during my sabbaticals

Usually in life, you first hear the legend about someone and, then, if you are lucky, you may meet the real person. I remember that among the first names I came across, as a PhD student in the field of amorphous semiconductors, was that of S. R. Ovshinsky. Terms like the “mobility edge,” the “Cohen, Fritzsche, and Ovshinsky (CFO) model” and the “Ovonic switching and memory devices” are very common in our field. Then I heard that Ovshinsky is “Mr.” and not “Professor” or even a simple “Dr.” and, most strangely of all, in every paper he mentions “his wife Iris” who accompanies him everywhere. “He must be a very interesting personality,” I thought, “apart from being a genius, he gives a lot of credit to women.” Now, more than 30 years later, after I had spent several sabbatical leaves in Energy Conversion Devices (ECD), Stan and Iris's company, and we had shared very personal thoughts next to their fireplace, I believe they were a remarkable couple that shared a deep, sincere love and a great admiration for each other. The sudden death of Iris in August 2006 shocked everyone and in particular Stan. A year later he decided to go on with his life; first by founding a new company (following his old dream 1) and then by marrying Dr. Rosa Young, a “unique, extraordinarily innovative talent,” as he characterized her several years earlier 2.

Stan has original thought and the ability to give simple solutions to complicated problems. He really is an “inventor.” He has the sharp mind needed to see below all the unnecessary theoretical wrappings and get down to the “bone marrow” of the problem. I understand that it may not be flattering for our ego, as university professors, but we have to admit that in certain cases self-teaching could be more successful than our teaching and several university degrees.

In 1977, the year that Prof. N. F. Mott got his Nobel Prize, I started my PhD at the Cavendish Laboratory, UK. At a celebration made in the laboratory in his honor, Stan Ovshinsky sent a huge bottle of champagne, more than 1 m high 3. This was my first indirect contact with Stan and the legend following him.

I first met Stan, in person, a few months later at the 7th International Conference on Amorphous and Liquid Semiconductors in Edinburgh where he gave a talk on “Chemical Modification of Amorphous Chalcogenides” 4. A new term, “modification,” was introduced in the field adding one more issue for discussions. At that time, the Amorphous Conferences were very alive, full of passion, arguments and, even, sometimes caustic comments. The critical question around for some time was: does glow-discharged Si contain hydrogen or not? A small scientific war between America and Europe was going on. Now, the “modification or doping” issue came to puzzle even more the amorphous chalcogenide community.

Anyway, the issue was intriguing and I was interested to try it as soon as possible. I ran back to Cambridge and put a bit of Ni in my sputtered a-As films. He was right, the modification worked. Even small amounts of Ni (<1.5 at %) change the room-temperature conductivity by five orders of magnitude 5. The resistance of the chalcogenide semiconductors could be controlled successfully 6. “Modification” and “alloying” worked well on chalcogenide semiconductor glasses and thin films but are different effects from the “doping” in a-Si:H, as the Fermi level remains close to the centre of the energy gap. These terms sometimes are still mixed up and used incorrectly by a lot of scientists in the field of chalcogenide semiconductors 7.

inline image MRS meeting, December 2004: Giving a tutorial. The periodic table of elements and the atomic models of amorphous compounds are everywhere around him, for inspiring his new scientific inventions.

2 Working in ECD during my sabbaticals

  1. Top of page
  2. Abstract
  3. 1 The legend and the personality of a self-taught genius inventor
  4. 2 Working in ECD during my sabbaticals

2.1 Reversible optical memory of chalcogenide alloys

I admit that I was impressed by his appearance in the conferences. I thought of him as a person that keeps people at a distance. But when I first joined ECD in 1984, working on “the reversible optical memory of the chalcogenide alloys,” with Dr. Rosa Young (now Rosa Ovshinsky), I realized that I had a completely wrong impression of him. He is a very sensitive and simple character, easily approached by everyone. He is a generous person that enjoys giving happiness to people surrounding him.

In ECD, I was impressed by several things. Stan and Iris cared for their employees and made them feel members of a big family. In every meeting the technicians were present and their opinions weighed a lot for Stan's decisions. They were treated with respect, “better than the scientists,” some people used to say. Stan strongly believes in “equal rights and equal opportunities” and as he does not want to forget his background (from a very young age he worked as a tool maker and machinist 8), he encouraged and supported the technicians to complete their education. Independent of status everybody was getting credit for their work. Any small achievements were celebrated, according to the saying “wine brings people together and breaks formalities.” Sometimes, in the evening, returning home you could find flowers or a basket with fruit waiting for you and a note: “Good work! Go on!” I still receive flowers on Christmas day and twelve red camations on May 1st.

The work was progressing very quickly. We had to meet deadlines. Our project had first priority. With Stan's signature any measurement needed was done at zero time and technicians were moved from different departments to work for us. What a difference from a university with limited resources. I believe that the amount of work done there during 6 months could be compared with 3 years' work in any “rich” university. The results were not published; instead they were used to file many patents, necessary to support Stan's independent research. We must recall that Stan filed the first patent in “phase-change memory” in 1968 9 when the amorphous semiconductor field was an infant.

inline image Fall 1991, in the gardens of Granboork Museum, MI. From left to right: Rosa Young, Genie Mytilineou, Stan & Iris Ovshinsky.

In 1982, Stan and Iris had founded the Institute for Amorphous Studies which offered an academic environment for ECD. Regular lectures were scheduled giving the excellent opportunity to meet Nobel Prize winners and famous scientists from USA, Japan, and Europe. Meetings were organized, by invited distinguished professors from all over the world, for exchanging ideas and proposing solutions to certain hot current issues. Publications such as “Institute for Amorphous Studies Series,” published by Plenum Publishing Co., offered a good reference literature to the field of amorphous semiconductors. Now, the Institute is the base of his new company “Ovshinsky Innovation LLC.”

2.2 Fluorinated amorphous silicon (a-Si:H:F) alloys

Most of the technical staff was working with Stan for years. Scientists come and go, but the technicians, the scientists in the Central Analytical Laboratory and the patent attorneys were always there, ready to recall in detail anything that was done in the company years ago. I could refer to a personal experience I had in 1991 when I spent a year in ECD. For the first few months I worked on a project on fluorinated amorphous silicon (a-Si:H:F) alloys with low defect density in the light-soaking saturated state.

In 1978 10, Stan, based on his chemical and structural concepts, had substituted hydrogen with fluorine in a-Si:H alloys for improving the degradation of solar cells; now he would like to work further on this topic. Everyone in the company who worked before in the a-Si:H:F project participated in daily “round table” discussions. At the end it was decided to use a small deposition chamber, with very strange electrode geometry and the nickname “mug.” This was the chamber where the first a-Si:H solar cell, with the record 13.8% efficiency, was fabricated more than a decade ago. The technician who designed and worked with it in the past dug out the “mug” (actually, it looked like one) and the patent attorney gave me the old notebooks containing more information that I needed. Too much unpublished knowledge was lying around. As it came out, “mug” was worth its good name. Stan was satisfied with the results. Fluorine proved to be a better defect compensator than hydrogen 11.

At that period, I also spent a few months in optimizing the efficiency of the roll-to-roll triple junction photovoltaic solar cells 2. I was impressed with the size of this production machine and the knowledge from different fields needed for building such equipment. I learned many things that were important in production and that I had not realized before doing university-type research. The knowledge was there, now I found a practical use for it. The roll-to-roll preparation technique requires peculiar limitations. The rolling speed and the chamber length define the thickness of each layer, for certain deposition conditions. Everything had to be optimized and calculated very carefully before the machine was built. After it is built, limited actions can be made for further optimization of the solar cell efficiency. The substrate temperature of each layer is another interesting example; it must be equal to or higher than the deposition temperature of the next layers. Unfortunately then, I realized that I had used relatively high substrate temperatures for the fluorinated films. So, one day, I said to Stan: “first, you had to ask me to work here, ‘put my feet to ground’ and then ask me to make a good fluorinated film for the machine.” Stan replied calmly: “don't worry, make a good material for me and I will build a machine for you.” Once more, I had realized that he really believed anything he was saying or promising to achieve, even when it sounded unrealistic to us. Stan does not follow the flow; he has the challenge and the strength to go upstream pulling us with him.

inline image 1991: Stan and Iris in front of the roll-to-roll solar cell production machine. One horizontal roll of film was deposited.

2.3 OUM memories

In the academic year 2003–2004 I visited ECD once more. This time Stan asked me to work in his more favorable invention: the “Ovonic memory,” a term found even in Webster's dictionary. The Ovonic electrically erasable programmable read only memory of the 1960s, after 40 years or so of unstopped research, had transformed to the submicron devices called “Ovonic universal memory” (OUM) and “Ovonic cognitive devices” 12, 13.

This time the basic research was on submicron devices. Photolithography was the dominant feature; everything else was related to it. Any small change in the deposition parameters of any layer could affect the photolithography process and the device performance. The challenge was to figure out what might go wrong at the 50 or more different process steps. But the results were fascinating. The tiny memory, cognitive, or threshold switching devices responded well with electrical or optical pulses 14, 15. If their properties were optimized they could make VLSI technology much simpler and faster, could be used in an electrical or optical cognitive computer or just used for encryption of data. The most fascinating of all were the cognitive devices 12–14. Their structural simplicity was amazing, but still they behaved like the biological nerves, able to make synapses.

A biological neuron cell receives electrical signals at its synaptic terminals, accumulates the energy until it reaches a threshold and then fires. In a similar way, the amorphous phase of the cognitive device accumulates energy from current pulses, changing the volume fraction of the microcrystallites into the amorphous phase, but not the electrical resistance, up to the percolation threshold where an abrupt reduction in resistance occurs when a microcrystalline path forms between the two electrodes. Usually the transition from the high resistance amorphous phase to the low resistance crystalline phase is achieved by providing a certain energy by means of a single current pulse of appropriate amplitude and duration. If, instead of a single current pulse, the same total energy was applied by a number of pulses of smaller duration, the material was also crystallized at the same low-resistance state. The intermediate partially crystallized states are stable until exposed to energy once again; they can also erase or we used reversibly as in the Ovonic memory devices. All the pre-threshold states, with resistance similar to that of the amorphous phase, form the region that is used for encryption of information. This is a simple and novel way to encode and store non-volatile information.

Stan and Iris were fascinating. Their research made cycles and was back to the beginning: neurobiology. They remembered their early research in neurophysiology and the nature of intelligence in mammals that brought them together years ago. Ironically their common life started with the research in neurons and finished with the cognitive device, an artificial neuron, almost 50 years later.

inline image 2003: The new generation roll-to-roll solar cell production machine. Four vertical rolls of films were deposited simultaneously. In the more recent version of this machine, up to six rolls can be deposited.

My memories for working with Stan will be incomplete if I do not mention the late Iris Ovshinsky: the woman next to the great man. A strong personality, always very calm and smiling, emitting love and care for everyone. I fully respected and admired her. Whenever they were asked “how the two of them managed to work so well together” they replied in one voice “by being in love.” The answer sounds simple, but everybody knows how difficult it is to find the true love and the deep devotion that Stan and Iris shared. Up to the end of their common life, they were able to forget all problems and found peace by being together and taking care of each other. Now Stan lives a new era, in work and private life. He is happy again. He found his balance at the new initial conditions that life drove him to. He is a “fighter” and proves it at any moment.

Numerous articles in magazines and newspapers referred to his efforts towards a “Green planet” without fossil fuel. To mention some of his inventions: solar cells, rechargeable NiMH batteries, batteries for electric cars, and solid H2 storage used as fuel on hybrid gas–electric cars 2, 12. The American broadcaster PBS (Public Broadcasting Service) in the series Nova (1987) characterized him “Japan's American Genius”; Time Magazine (1999) “Hero of the Planet” and The Economist (2006) is wondering if he is the “Edison of our Age?” Whenever asked he replies: I never did this for awards, money or power. I did it because it had to be done, and because of my social drive to make a better and more beautiful world. That's what I started doing when I was knee high, and I do not expect to stop now.

Stan, on your birthday, we wish you to keep showing us the way towards a nicer and cleaner world; do not stop inspiring us with your innovating work.

  • 1
    H. Fritzsche and B. Schwartz (eds.), Stanford R. Ovshinsky: The Science and Technology of an American Genius ( World Scientific, Singapore, 2008), selected publications.
  • 2
    S. R. Ovshinsky, Mater. Res. Soc. Symp. Proc. 554, 399 (1999).
  • 3
    E. A. Davis (ed.), Neville Mott: Reminiscences and Appreciations ( Taylor & Francis, London, 1998), Plate 6.
  • 4
    R. Flask, M. Izu, K. Sapru, T. Anderson, and S. R. Ovshinsky, in: Proc. 7th Int. Conf. Amorphous and Liquid Semiconductors, Edinburgh, edited by W. Spear (CICL, University of Edinburgh, 1977), p. 632.
  • 5
    E. A. Davis and E. Mytilineou, Sol. Energy Mater. 8, 341 (1982).
  • 6
    S. R. Ovshinsky, in: edited by D. Adler, B. B. Schwartz, and M. C. Steele, Physical Properties of Amorphous Materials ( Plenum Press, New York, 1985), p. 105.
  • 7
    E. Mytilineou, J. Optoelectron. Adv. Mater. 4, 705 (2002).
  • 8
  • 9
    S. R. Ovshinsky, Method and Apparatus for Storing and Retrieving Information, US Patent No. 3 530 441, applied for Aug. 22, 1968 and issued Sept. 22, 1970.
  • 10
    S. R. Ovshinsky and A. Madan, Nature 276, 482 (1978).
  • 11
    X. Deng, E. Mytilineou, R. T. Young, and S. R. Ovshinsky, Mater. Res. Soc. Symp. Proc. 258, 491 (1992).
  • 12
    S. R. Ovshinsky, Jpn. J. Appl. Phys. 43, 4695 (2004).
  • 13
    S. R. Ovshinsky and B. Pashmakov, Mater. Res. Soc. Symp. Proc. 803, 49 (2003).
  • 14
    S.R. Ovshinsky, in: Proc. 7th Int. Symp. Optical Storage, China, 2005, edited by F. Gun and L. Hou (Proc. SPIE 5966) (SPIE, Bellingham, 2005), p. 1.
  • 15
    E. Mytilineou, S. R. Ovshinsky, B. Pashmakov, D. Strand, and D. Jablonski, J. Non-Cryst. Solids 352, 1991 (2006).