NEC and NEC Electronics Develop High Threshold Voltage Control Gallium Nitride (GaN) Power Transistor on a Silicon (Si) Substrate
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.
Tweet-- 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.
