NEC Corp announced Sept 24, 2013, that it has developed a carbon nanotube (CNT) transistor capable of operating at a frequency of 500kHz or higher.

"The performance of the transistor is high enough to be used for the line control circuit of a flexible display or sensor sheet," the company said.

NEC will disclose the details of the transistor at 2013 International Conference on Solid State Devices and Materials (SSDM 2013), an academic conference on semiconductor technologies, which runs from Sept 25 to 27, 2013, in Fukuoka City, Japan.

NEC has long been engaged in the development of a technology of forming a CNT transistor with a coating process. However, the performance of its CNT transistor had not improved to a high enough level for commercialization for a long time. Especially, it had problems related to on/off ratio and output current.

1/10 parasitic capacitance, 10x output current

NEC made two major improvements. First, the company employed the "Super Ink-jet (SIJ) Method" to form electrodes and reduced their width from about 50μm to 2μm. As a result, the overlapping of gate electrodes and source/drain electrodes was reduced, decreasing parasitic capacitance by 90% and drastically increasing operating frequency.

Second, NEC greatly improved the accuracy of separating semiconductor-type CNTs from metal-type CNTs. The company previously used a method that improves the purity of semiconductor-type CNT to 95% or higher. But the dispersion stabilizer used for the separation process remained as an impurity, affecting the performance of the transistor.

This time, NEC improved the purity to 98% or higher while reducing the amount of the remaining dispersion stabilizer by 98%. As a result, the quality of the transistor's semiconductor layer was drastically improved, increasing output current, for example, from -0.6μA to -6.2μA.

NEC will disclose the on/off ratio and carrier mobility of the transistor at the SSDM. They have been improved to a high enough level for commercialization, the company said.