AIST researchers have developed a graphene transistor with a new operating principle. In the developed transistor, two electrodes and two top gates are placed on graphene and graphene between the top gates is irradiated with a helium ion beam to introduce crystalline defects. Gate biases are applied to the two top gates independently, allowing carrier densities in the top-gated graphene regions to be effectively controlled. An electric current on/off ratio of approximately four orders of magnitude was demonstrated at 200 K (approximately −73 °C). In addition, its transistor polarity can be electrically controlled and inverted, which to date has not been possible for transistors. This technology can be used in the conventional production technology of integrated circuits based on silicon, and is expected to contribute to the realization of ultra-low-power-consumption electronics by reducing operation voltage in future.
In the developed transistor, the on state or off state is controlled according to whether the polarities of the voltages applied to the two top gates are the same or different. Therefore, by fixing one gate bias and changing its polarity, it is possible to control whether the transistor operation by sweeping the other gate voltage is n-type or p-type. In the present experiment, voltages of −100 mV and +100 mV were applied to the source and drain terminals, respectively.
The transistor polarity of conventional silicon transistors is determined by the type of ion for doping, so it is not possible to change the polarity once a circuit is formed. However, because the polarity of the developed transistor can be electrostatically controlled, it is possible to realize an integrated circuit whose circuit structure can be electrically changed.
The researchers are aiming to realize CMOS operation in which transistor polarities can be changed through electrical control. They are also aiming to create a device prototype using a large-scale wafer with graphene synthesized by the CVD method (chemical vapor-phase deposition method). At the same time, efforts to achieve higher-quality graphene will be made in order to improve the on/off ratio of electric current at room temperature and carrier mobility.