Communications of the ACM
The Messy Path to Transparent Electronics
Clearly transparent: Oregon State development engineer Chris Tasker (left), Professor Emeritus John Wager (center), and Professor of Chemistry Douglas Keszler (right) hold arrays of transparent transistors on a glass substrate.
Credit: Gary Oakley
John Wager worked part time at a gas station in the early 1970s filling tanks and washing windshields, while attending high school in Southern California. One day, while fueling up, an older man asked Wager what he planned to do with his life. When Wager said he was considering a career in engineering, the man replied, "Well, you'll most likely spend all that money going to school and then be unemployed the rest of your life."
Although at the time some people believed there wasn't much of a future in engineering, Wager took the man's comments as a challenge—a move that paid off beyond his wildest dreams.
If you use a laptop, a tablet, or a smartphone, you have held the results of Wager's groundbreaking, collaborative research in your hands.
Although you can't see it, because it's transparent.
Wager, who retired in 2017 as the Michael and Judith Gaulke Chair of Electrical Engineering and Computer Science at Oregon State, played a critical role, with an interdisciplinary team of researchers, in developing the world's first transparent transistor—a breakthrough that is moving well beyond digital display devices.
Transparent electronics are poised to transform windows and other glass surfaces into electronic interfaces of all sorts. Imagine Venetian blinds that are integrated inside window glass and can be activated to block sunlight with the touch of a finger against the pane. Or a kitchen window that displays recipes, timers, temperatures, and other tools—all with the tap of a finger—while letting in light like any other window. Or smart automotive glass, solar panels, and bathroom mirrors that can display alerts, energy usage, appointment reminders, and other information.
The Clock is Ticking
Wager earned his undergraduate degree in engineering physics from Oregon State in 1977, then his master's and doctoral degrees in electrical engineering from Colorado State University. After graduate school, Wager worked for two years at Hughes Research Labs in Malibu, Calif., where he conducted research on high-speed semiconductors.
In 1984, he returned to his Oregon alma mater and joined the faculty in the Department of Electrical and Computer Engineering. Today he refers to his first Oregon State position, that of assistant professor, as "The hardest job in the world, because you have to learn everything right away—how to teach, find research money, and mentor students—and the clock is ticking the whole time."
At Oregon State, Wager continued his research on high-speed semiconductors. From 1988 to 2000, he collaborated with Beaverton-based Planar Systems on using thin-film electroluminescence in displays. Although liquid crystal displays eventually eclipsed electroluminescence technology, Wager would later tap his experience with Planar Systems as he worked to develop a transparent transistor.
In 2001, Wager teamed up with Oregon State physics professor Janet Tate, and chemistry professors Douglas Keszler and Arthur Sleight.
"We'd been talking for a year or two, trying to figure out a way the four of us could work together on a project," Wager said.
But it wasn't until Tate came across a paper published by researchers at the Tokyo Institute of Technology about developing p-type transparent conductors that the group found a research focus that resonated.
"We thought, 'Aha! This is the project we've been looking for,'" Wager said. "Maybe we can come up with some interesting materials that are both transparent and conductive."
As inorganic chemists, Keszler and Sleight understood where to go on the periodic table to get to the chemistry for this sort of project. "That was something no engineer or physicist would have known, and Janet was interested in synthesizing and characterizing thin films, and I was interested in thin-film-device applications. So as a group we agreed to try to make some sort of electronic device using the p-type materials we hoped to develop," Wager said.
The team secured research funding from the U.S. Army Research Office and the National Science Foundation and dove in: Keszler and Sleight were developing the materials while Tate and Wager tried to make thin films out of them. But the work was much more challenging than they anticipated, and many of the materials they developed were neither transparent nor conductive.
"The p-type materials were horrible, and we were about a year in," Wager said. "So we had a meeting around Thanksgiving of 2001 and said, 'Okay, let's think about this.' Based on our work with Planar Systems, we knew a lot about n-type transparent conductive oxides and glass substrates, so we pivoted toward that."
They started working with zinc oxide, and thanks to Randy Hoffman, a "wickedly smart" master's student of Wager's who spent most of his winter holiday working in the lab, they had a demonstration of the world's first transparent transistor by the end of the year.
"We just took a different fork in the road, but that wasn't until we were very frustrated with our initial approach," Wager said. "In research, the best things that happen often involve the detours we take, which is why I encourage students to exercise their creativity and explore other directions."
In 2003, when the team announced the invention of the transparent transistor, the media had a heyday. "They were bewildered and had a hard time getting their mind around an invisible electronic switch made from zinc oxide, the same mineral sold as the white cream you lather up with in order to protect yourself from the sun when you go to the beach," Wager said.
Although Wager predicted that zinc oxide transistors might be used as pixel switches in flat-panel displays, that didn't ultimately happen. But something else did.
Happy Combo
The group licensed the technology to Hewlett-Packard Co. (HP) and started a joint-development program to take the transparent transistors to the next level. But within six months, they "stumbled onto" another class of materials called amorphous oxide semiconductors, which worked much better than zinc oxide, and included a range of material combinations, for example, zinc tin oxide (ZTO), indium zinc oxide (IZO), and indium gallium zinc oxide (IGZO).
For the next few years Wager and his colleagues filed numerous patents and collaborated with HP on the R&D. The display industry was intrigued, but cautious. At the time, amorphous hydrogenated silicon was the go-to material used for backplane transistors in the $100 billion flat-panel-display industry. But as display technology advanced, adding more and smaller pixels and larger and larger screens, amorphous hydrogenated silicon was becoming less ideal. The industry knew this and had been pouring billions of research dollars into developing a replacement material called low temperature polycrystalline silicon, or LTPS. They didn't see what was coming from Wager and his team.
"The industry had been working on LTPS for two decades, and the plan was to smoothly transition from amorphous silicon to LTPS," Wager said. "But then this disruptive technology we had developed came along and really mucked things up for LTPS, because all of the sudden, you had another choice."
It turns out the amorphous oxide semiconductor made of indium gallium zinc oxide has some advantages over LTPS, including lower cost, reduced power, and the ability to scale to larger display sizes.
And that's where things stand today. IGZO is going head-to-head with LTPS in the large-display industry, and Wager has his money on IGZO.
He points to the Apple iMac with 5K retina display sitting on his desk. "That computer has 14.7 million IGZO pixel-switching transistors," he said. Apple and other American companies like Applied Materials and Corning are key players in the race.
THE IMPACT ON PEOPLE
During his career, Wager has attracted approximately $20 million in research funding to Oregon State. He wrote the first book on transparent electronics and has mentored more than 80 graduate students. At least one of those students, Randy Hoffman, the master's student who worked through winter break to demonstrate the first transparent transistor, is grateful for his relationship with Wager.
"As I was nearing the end of my senior year at Oregon State, John encouraged me to pursue a graduate degree in solid state materials and devices," Hoffman said. "This was a different direction than I had been heading at the time, and I'm grateful for John's encouragement to consider a course change."
No doubt. Hoffman currently has more than 50 U.S. patents to his name and is a senior engineer in technology development at HP.
"John's been a dependable innovator, collaborator, and advocate for oxide transistor technology, through direct research in his group at Oregon State and many associated industry and academic partnerships," Hoffman said.
Through a licensing agreement of the technology to HP, Wager's work has brought him and Oregon State financial gain. Approximately $3 million of the royalty funds generated to date have been used to set up an endowment to help support Oregon State's Materials Synthesis and Characterization Facility.
"A significant fraction of the royalty money generated has been reinvested into OSU," Wager said. "Hopefully it will pay dividends, and in five or ten years we'll hear about another interesting development that one of our new faculty has come up with."
In 2012, Wager's work was recognized by Oregon State alumni Mike and Judy Gaulke, whose $3.5 million gift funded the largest endowed faculty position in the College of Engineering and the first endowed chair in the School of Electrical Engineering and Computer Science. Wager was the inaugural holder of the Michael and Judith Gaulke Chair of Electrical Engineering and Computer Science until his retirement.
"This endowed chair was our first major gift," Michael Gaulke said. "Judy and I hope it can be used to continue to grow the prestige and reputation of Oregon State's School of Electrical Engineering and Computer Science and to help inspire more philanthropists to do the same." Gaulke has served in executive positions at McKinsey & Company, Spectra Physics Inc., Raynet Corp., and Exponent Inc. "It's going to be hard to match the success that John has had in that position, because we've clearly hit a home run with the first holder of the chair, in terms of what he's been able to do," he said.
Instead of a home run, perhaps winning the World Series is a more fitting metaphor, given the impact that Wager's work has had—and will continue to have—on the world of electronics, glass surfaces, and potentially plastics and other substrates.
Recently inducted into the National Academy of Inventors, Wager is also an IEEE Fellow and a Society for Information Display Fellow.
Looking back, it's clear that Wager made the right call when he chose a career in engineering. He took on the challenge and the rest is history.
"What happened with our work is beyond my wildest imagination," Wager said, shaking his head. "Twenty years ago, I never thought I'd see anything I was doing end up inside a commercialized product, ever. It's pretty rare, and not only in one product but a wide range of products for a $100-billion-a-year industry. I'm astonished, because I didn't set out to do that—but sometimes you just get lucky."
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