tailieunhanh - Carbon Nanotubes – A scientometric study_2

Tham khảo sách 'carbon nanotubes – a scientometric study_2', kỹ thuật - công nghệ, hoá học - dầu khí phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 13 Measurement of High-Frequency Characteristics of CNTFETs and Equivalent Circuit Model Analysis Kaoru Narita NEC Corporation Japan 1. Introduction Carbon nanotube field effect transistors CNTFETs are high-mobility devices that operate at very high-speeds. Theoretical analyses suggest that the cut-off frequency fT of an ideal CNT-FET is between 800 GHz and THz when its gate length is pm 1 2 . Since this frequency is much higher than that of state-of-the-art Si GaAs and InP transistors CNTFETs are promising candidates for future nanoelectronic devices. Singh et al. 3 measured frequency responses of top-gated CNTFETs up to 100 MHz. Li et al. 4 observed operation of CNTFETs with an LC impedance-matching circuit. However as Li et al. pointed out 4 measuring high-frequency performance of high-impedance devices such as CNTFETs is quite difficult. This is because their output impedances are much higher 105 Q than the impedance of the measurement system 50 Q using a network analyzer. To perform accurate high-frequency measurements especially those to determine fT values of such devices we must measure S-parameters with a network analyzer even though large impedance mismatches hinder us from obtaining accurate measurement data. Kim et al. 5 measured S-parameters of multifinger CNTFETs by using a network analyzer and obtained an fT value of GHz. They also concluded a maximum oscillation frequency fmax of more than 5 GHz was obtained using the maximum stable gain Gmsg . Le Louarn et al. 6 obtained intrinsic fr value of 30 GHz by measuring a CNTFET the channel of which was fabricated using dielectrophoresis to increase the CNT density. They also obtained Gmsg value of more than 10 dB at 20 GHz. This chapter will describe a method for accurately measuring and modeling the high-frequency characteristics of CNTFETs with reference to our experiment and analysis 7 . In the experiment we first decreased the device impedance to be able to measure the S-parameter