Bizen Transistor Holds Promise for Replacing CMOS

Article By : Sally Ward-Foxton

British startup Search For The Next to further develop CMOS-alternative as part of UK’s cleantech strategy...

Search For The Next, the British startup with the new transistor design that it says will “consign CMOS to the history books,” has received an award of £1.7m (about €1.9m) from the UK government. The grant, from the UKRI’s Industrial Strategy Challenge Fund, will allow further development of the transistor’s enabling process technology.

“We are extremely pleased that the UK government has recognized the key role that Bizen will play in enabling the UK to meet its ambitious net zero targets,” said David Summerland, CEO of Search For The Next (SFN). “Bizen [enables] the UK to develop a leadership position in semiconductor manufacturing. My challenge to the industry is this: have a look at Bizen and we are sure you’ll see that it’s impossible to produce a wide variety of ICs at a lower cost or on a shorter [time to market]. Truly, CMOS is history.”

The Bizen transistor is a combination of a bipolar junction transistor and a Zener diode (Image: SFN)

Search For The Next’s Bizen transistor design, a combination of a bipolar junction with concepts from a Zener diode, uses the quantum tunneling effect to eliminate the resistor, and all the metal layers, from a traditional bipolar transistor. The transistor’s gate uses a quantum tunneling connection; in fact, multiple gate connections can be made, meaning multiple NOR and OR gates can be created inside one transistor, with a resulting die shrink for logic circuits.

Summerland, in a previous interview with EE Times, said that the Bizen transistors can match or beat the switching speed and dynamic power of CMOS process technologies, though there is some static power requirement. Bizen also does not suffer from CMOS’ electrostatic discharge (ESD) susceptibility and latch-up problems. Bizen transistors are applicable to both digital transistors and power devices.

NOR gates created by (left) a single Bizen transistor, (center) CMOS transistors (note that the left hand side of the circuit is for ESD protection, which is not required by the Bizen version), and (right) the equivalent circuit in TTL. (Image: SFN)

The original aim was to create a chip with a low number of mask steps that could have both logic and power transistors on the same die, with the original intention of creating an LED driver IC. Summerland hit upon the idea of using the reverse bias characteristic of a Zener diode, which is produced by the abrupt change in doping levels between the n and p layers of the diode. This results in the generation of a quantum current. Summerland wanted to use that current to drive a bipolar transistor.

Since only 4-8 mask layers are required (compared to 10-17 for CMOS), Bizen devices can be produced quickly and economically at relatively large process nodes suitable for the UK’s low capex fabs. Lead time, according to SFN, is reduced from 15 weeks to 3 weeks. SFN has been working with semiconductor and MEMS fab Semefab in Scotland, but the process would be transferrable to other fabs such as Newport Wafer Fab (compound semiconductor process) in Wales.

“What came out of that is actually a very elegant process architecture with relatively few diffusions and only eight masks,” said Allan James, Managing Director, Semefab. “Eight masks can create Bizen devices capable of performing logic functions, also lateral devices which are capable of performing analogue functions, and also the vertical npn power transistor function.”

Comparison between Bizen and CMOS flip-flop circuits

Equivalent flip flop circuits showing the space saved using Bizen transistors (right) and CMOS MOSFETs (left). (Image: SFN)

Semefab, established in Glenrothes, Scotland for 33 years, operates three fabs including two MOS/bipolar facilities (one processing 100mm wafers at the 1µm node, and one processing 150mm wafers at the 1µm node with stepper capability down to 0.7µm), plus a specialised MEMS fab.

The foundry will run further Bizen tests, increasing the level of integration and performing further characterisation including accelerated life testing. Yield statistics, said James, are also not yet available, but he pointed out that so far the Bizen transistors have appeared uniform across their 150mm wafer and that sampling large numbers of devices at random indicated that this is a uniform effect.

Regarding the technology’s potential for scalability, James said that the nature of the individual process steps gives the technology an innate ability to scale to smaller nodes.

As part of the “Driving the Electric Revolution Challenge” program, SFN’s grant is part of the UK’s strategy to capitalize on global opportunities in cleantech and electrification. SFN is one of more than 30 partner research and technology organisations that will collaborate in new Industrialization Centers announced by the UK government.

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