Electronics, especially custom silicon, is a long and laborious process. The time required to construct and fabricate a new chip, even a simple one, can take months and requires dozens of fabrication steps, each wrought with the potential for failures.
A new collaboration between a Nottingham-based startup (SFN) and a UK-based fab (Semefab) has developed a completely new type of transistor that makes fabrication easy. This means faster fabrication of chips and shorter design times. In short, it’s the dream of any silicon engineer.
In effect, this new transistor is a bipolar transistor with all the metal layers stripped away, with the input of the transistor controlled by quantum tunneling, something usually seen in a Zener diode. A Zener diode is just like a normal diode, but allows current to flow when a voltage exceeds a set point thanks to quantum tunneling.
With numerous but little-used exceptions, most transistors come in two varieties: the FET transistor, and the BJT transistor. Of these, the FET, or more specifically the Metal Oxide FET transistor, is used for most applications, from power supplies to the transistors that make up a computer chip. This new transistor, called a ‘Bizen’ transistor is completely unlike either of these, and that’s what makes this new transistor so exciting.
A simple part of a chip, for example a NAND or NOR logic gate, is usually constructed with a dozen or so process layers. For each of these layers, Silicon must be stripped away, doped, ions implanted, metal applied, and constructed in three dimensions just a few atoms at a time. Because this new process does not require metal layers, a simple gate can be made with just four mask layers.
While these new transistors are slightly odd in their construction, the real takeaway here is how simple it is to construct a transistor. A simple IC with a handful of gates has a dozen or so layers, with dozens more steps during the fabrication process.
A complex IC, like a modern CPU or a memory, can have over a hundred layers and thousands of steps to make a single wafer full of chips. The Bizen requires only four mask layers, and is relatively simple to produce.
The net effect of this new technique of making transistors is that new, novel chips can be made faster and cheaper, allowing for rapid testing and manufacturing.
Further tests are needed for devices constructed out of Bizen transistors. While the first wafers have already been fabricated, they’re undergoing testing to completely characterize the transistor and the yield of the wafer.
Further down the road, more wafers will be created to determine the yield statistics and maneuverability. From there, it’s a matter of commercializing the process and producing standard libraries, which should be ready by the middle of next year.