The technology that will power future transparent flat displays is continuing to be developed at OSU. Last month researchers in the OSU Engineering department published another paper in the field pioneered at OSU, transparent electronics like the kind found in LCD flat panel displays. The research focused on whether or not zinc tin oxide (ZTO), an amorphous oxide semiconductor used for thin film transistors, is useable for the creation of memristive devices like RRAM.
So what is a memristor you ask? According to HP’s FAQ on memristors, “a memristor can be thought of as a pipe that expands or shrinks when water flows through it. If the water flows through the pipe in one direction, the diameter of the pipe increases, thus enabling the water to flow faster. If water flows through the pipe in the opposite direction, the diameter of the pipe decreases, thus slowing down the flow of water. If the water pressure is turned off, the pipe will retain it most recent diameter until the water is turned back on. Thus, it remembers how much water flowed through it.”
In this case, the kind of “memristor” being developed is a form of Resistive Random Access Memory (RRAM). According to John Conley, Professor of Electrical & Computer Engineering at OSU, instead of using electronic charge, RRAM devices use a change in electrical resistance to generate the 1s and 0s necessary for memory storage. An RRAM memory element is a two terminal device, consisting of 2 perpendicular crossbars lines of metal going in opposite directions with a layer of RRAM material separating them. One bit of memory is stored in the RRAM material at the intersection between cross bar
At present, amorphous silicon is being displaced by iridium gallium zinc oxide (IGZO) transistors for high performance display applications. According to a press release from Sharp, an electronic manufacturer, “Employing advanced IGZO oxide semiconductors enables Sharp to produce LCDs with smaller thin-film transistors and increased pixel transparency, thus allowing for lower energy consumption.”
One of the benefits of IGZO, over traditional amorphous silicon thin film transistors, aside from being transparent, is that the electron mobility is ten to twenty times faster. The increased mobility means that less energy is required to move any given electron and therefore electronics can be made smaller, faster, and more power efficient.
A potential replacement for IGZO is ZTO. ZTO offers similar performance to IGZO with the advantage of using zinc and tin instead of indium and gallium, elements which are more common and potentially cheaper. In addition, the same tooling used for IGZO could be used for ZTO. This could dramatically cut down on the amount of time it takes for research to get out of the lab, into private manufacturing fabs, and eventually into consumer products.
What the OSU researchers have done is shown that ZTO can be used for not only for thin film transistors, but also for memristors. Beyond just traditional LCD screen these kinds of memristive circuits could eventually prove useful in the production of flexible displays of the kind drooled over by tech geeks.
Furthermore, research is being done at other institutions on whether or not memristance could be analogous to the kind of information processing done in neurons. Imagine a world where your phone or tablet isn’t just light, but is capable of complex creative computation and is also capable of being rolled up and put in your pocket. That world may not be that far away and it could be research from institutions like OSU that will help get us there.
by William Tatum