NEC and NEC Electronics Develop High Threshold Voltage Control
Gallium Nitride (GaN) Power Transistor on a Silicon (Si) Substrate
New Delhi, December 11, 2009: NEC Corporation (NEC) and NEC Electronics Corporation (NECEL)
today announced the development of a nitride semiconductor (*1) power transistor on a silicon
(Si) substrate that has improved the control and suppression of electrical currents
when electrical power is turned off (normally-off characteristics (*2)), a necessary feature for
the safe operation of consumer electronics and IT devices. The transistor features a new
structure for the layer beneath the gate electrode, which improves the controllability
of threshold voltage that intercepts electrical currents and enables the realization of low-power
losses, high speed switching and high temperature operations.
Power transistors that use silicon semiconductors occupy an important role in the advancement
of energy conserving machines, as they convert electrical power and serve as a controlling
element for a wide range of applications, from consumer electronics to industrial machinery.
Future expectations are high for the implementation of Nitride semiconductor transistors,
which demonstrate lower-level losses, higher speeds and higher temperature operations when
compared to current silicon transistors. However, it is important to suppress variations of
threshold voltage and improve reproducibility of their normally-off characteristics.
Current transistors are composed of a two-layer structure that consists of an AlGaN electron
supply layer and GaN channel layer. A great deal of variation in threshold voltage occurs due to
differences in the thickness of the AlGaN electron supply layer under the gate, which is etched
down to a few nm from 20-30 nm to achieve normally-off characteristics. A high precision
etching process is specifically required in order to reduce the variation of threshold voltage
and stabilize normally-off characteristics.
A five layer structure makes it possible for these new transistors to control threshold voltage
with a high degree of precision by reducing the threshold voltage's dependence on the
thickness of the electron supply layer. This is accomplished by introducing an electric charge
neutralization layer, the "piezo" neutralization layer, within the electron supply layer, while at
the same time introducing a buffer layer, located beneath the channel layer, with the same
composition as the piezo neutralization layer. This structure enables uniform manufacturing of
nitride semiconductor power transistors that realize normally-off characteristics at a low cost.
These transistors also exhibit excellent performance such as low power loss and
high breakdown voltage.
Looking forward, NEC and NEC Electronics aim to accelerate research and development
towards the design, evaluation and implementation of nitride semiconductor power
transistors.
NEC will present transistor results at the International Electron Devices Meeting (IEDM) held in
Baltimore from December 7, 2009 (announcement on December 7).
(*1) Nitride Semiconductor: Semiconductors composed of Gallium nitride (GaN)/aluminum
nitride gallium (AlGaN) that have bandgaps larger than 3.4eV. These promising devices feature
high breakdown field strength and high electron mobility, as well as components that produce
high power output and resist high temperatures and voltage. Th ese semiconductors are widely
used by Blue LED materials that capitalize on large bandgaps.
(*2) Normally-Off Characteristics: Characteristics that block electrical currents when voltage is
not applied to a transistor. This is necessary for the safe operation of machinery and tools.
About NEC Corporation
NEC Corporation is one of the world's leading providers of Internet, broadband network and enterprise
business solutions dedicated to meeting the specialized needs of a diversified global base of customers.
NEC delivers tailored solutions in the key fields of computer, networking and electron devices, by
integrating its technical strengths in IT and Networks, and by providing advanced semiconductor
solutions through NEC Electronics Corporation. The NEC Group employs more than 140,000 people
worldwide. For additional information, please visit the NEC website at: http://www.nec.com.
About NEC Electronics
NEC Electronics Corporation (TSE: 6723) specializes in semiconductor products encompassing advanced
technology solutions for the high-end computing and broadband networking markets; system solutions
for the mobile handset, PC peripheral, automotive and digital consumer markets; and multi-market
solutions for a wide range of customer applications. NEC Electronics Corporation has subsidiaries
worldwide including NEC Electronics America, Inc. and NEC Electronics (Europe) GmbH. More information
about NEC Electronics worldwide can be found at www.necel.com.
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trademarks of their respective owners. ©2009 NEC Corporation
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