Researchers in Japan have created the first "n-channel" diamond-based transistor, inching us closer to processors that can operate at super-high temperatures. This eliminates the need for direct cooling and increases the range of environments where processors can operate.
By using diamond in a transistor — electrical switches that flip between 1 and 0 when voltage is applied — the research opens up the prospect of electronics that are smaller, faster and more power-efficient.
They can also work in much harsher environments than conventional components — operating in temperatures above 572 degrees Fahrenheit (300 degrees Celsius) rather than the typical transistor's limit of 212 degrees Fahrenheit (100 degrees Celsius) — and can endure much higher voltages before breaking down.
The scientists detailed their findings in a paper published Jan. 19 in the journal Advanced Science.
Silicon transistors have been used to make processors since the early 1960s, but it's reaching its physical limitations as the size of the manufacturing process (as low as 3 nanometers) approaches the 0.2-nanometer width of silicon atoms.
There are several different types of transistors out there, but the most commonly used is metal-oxide-semiconductor field-effect transistor (MOSFET), with "metal-oxide-semiconductor" referring to the silicon wafer of a conventional computer chip.
Within MOSFETs, there are different configurations too — referred to as n-channel and p-channel. N-channel transistors use electrons to carry charge while p-channel transistors use "holes" — that is, in greatly simplified terms, the gaps left behind by escaped electrons. N-channel transistors are commonly found in high-side power switches to protect batteries.
In the new study, the researchers built a transistor with two "phosphorus-doped diamond epilayers." Phosphorus doping, which simply means adding the element to the layers, is necessary to add conductivity. This is the n-channel layer, which carries free electrons and would replace the silicon-based layer in a conventional chip. When enough electrons flow, they connect two ends of a gate — known as "the source" and "the drain." This closes the circuit to represent a 1 rather than a 0.
The team lightly doped the negative layer with phosphorus and heavily doped the second, positive layer. The scientists then formed annealed titanium "source" and "drain" contacts on the top, heavily doped layer, before adding 30-nanometer-thick aluminum trioxide to serve as an insulator. The result was the world’s first working n-channel MOSFET transistor made using diamond.
The researchers then put the transistor through a series of tests to check for conductivity performance. "The n-type diamond MOSFETs exhibit a high field-effect mobility around 150cm2/V/sec at 573K," they said in their paper, referring to high conductivity and stability at extremely high temperatures. This was "the highest among all the n-channel MOSFETs based on wide-bandgap semiconductors," they noted.
A bandgap, measured in electronvolts (a unit of kinetic energy) is an area within the n-channel in which valence electrons (those in an atom's outermost shell) can move freely. A wider bandgap means a component can operate at higher voltages and frequencies. Diamond has a 5.47eV bandgap compared with 1.12eV for silicon.
This is not the first diamond transistor breakthrough. Another team published a study in January 2022 in the journal Nature detailing how to create diamond-based p-channel wide-bandgap transistors. Until now, scientists have been unable to demonstrate a working n-channel diamond-based transistor.
When it comes to future applications for their transistor, the scientists suggested it could work in energy-efficient electronics, as well as spintronic devices and sensors made from micro-electromechanical systems (MEMS) that can operate in harsh environments, such as space.
There are other uses for diamond semiconductors, including in supercomputers, electric vehicles (EVs) as well as lighter and more durable consumer electronics.
