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III-V materials lead to highest-performance MOSFETs

Posted: 17 Jun 2014     Print Version  Bookmark and Share

Keywords:Semiconductor Research  MOSFET  silicon  III-V material  InGaAs 

Researchers at the 2014 VLSI Symposium in Honolulu, Hawaii have revealed that the highest-performance metal-oxide-semiconductor field-effect-transistor (MOSFET), if not the fastest, is no longer made from silicon. Instead, it's made from III-V materials grown over a silicon substrate.

In a demonstration supported by the Semiconductor Research Corp., researchers from the University of California at Santa Barbara (UCSB) showed what they called the world's highest-performance MOSFET formed from indium-gallium-arsenide (InGaAs) atop indium-phosphide (InP), which can be grown on silicon (Si).

"The present substrate is InP. Other research groups, including IMEC, have shown that InP can be grown on Si," said Mark Rodwell, professor of electrical and computer engineering at UCSB. "There is, indeed, at least one InGaAs-on-Si III-V MOS presentation at the VLSI Symposium. So, although our record devices are not on Si, it can certainly be done."

Transmission electron microscopy of the MOSFET

Transmission electron microscopy shows a 2.7nm channel, sophisticated high-K dielectric, and other advanced features that researchers say make this the world's highest-performing MOSFET. (Source: UCSB)

Not only did the III-V MOSFETs deliver higher performance than similar sized silicon transistors, but they also consumed less power. According to Rodwell, they will eventually overtake silicon FinFET transistors in speed and power consumption.

Even though the researchers have not measured switching speed yet, they estimate that, for RF/wireless applications, the III-V MOSFETs will run 30-60 per cent faster than silicon RF. And since electron mobility is 2.5-3 times faster in InAs than Si, digital clock speeds are estimated to be significantly higher than Si.

For now, the "highest-performance" claim is based on the on-current (0.5 milliamps per micron width) and off-current (100nA) of UCSB's III-V MOSFETs when produced in similar sizes and gate lengths (25nm) and when operating at similar voltages (0.5V) to Si. Rodwell said future versions of the III-V MOSFET will significantly outperform silicon FinFETs of equal size.

Architecture of the metal gate III-V MOSFET

Detailed layered architecture of the metal gate III-V MOSFET that researchers said outperforms silicon MOSFETs. (Source: UCSB)

The tricks Rodwell's group used were based on fabricating the InAs semiconductor channels just 2.5nm thick. Doctoral candidate Cheng-Ying Huang accomplished that feat together with Professor Arthur Gossard.

Doctoral candidate Varista Chobpattana, working with professor Susanne Stemmer, built sophisticated high-k gate dielectrics, stacks of nickel-aluminum (NiAl) metal gates on layered stacks of alumina (Al2O3 on InAa) and zirconia (ZrO2) with very high capacitance density, thus enabling the high turned-on currents.

The final touches were applied in Rodwell's lab by doctoral candidate Sanghoon Lee, who designed the MOSFET adding a vertical spacer layer to cut current leakage by smoothly distributing the electric field so as to avoid band-to-band tunneling. The researchers said this produces off-currents that rival modern silicon MOSFETs.

- R. Colin Johnson
  EE Times

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