IEEE ELECTRON DEVICE LETTERS, VOL. 24, NO. 3, MARCH 2003 189 What are the Limiting Parameters of Deep-Submicron MOSFETs for High Frequency Applications? G. Dambrine, Member, IEEE, C. Raynaud, D. Lederer, M. Dehan, O. Rozeaux, M. Vanmackelberg, F. Danneville, Member, IEEE, S. Lepilliet, and J.-P. Raskin, Member, IEEE Abstract—Parameters limiting the improvement of high frequency characteristics for deep submicron MOSFETs with the downscaling process of the channel gate length are analyzed experimentally and analytically. It is demonstrated that for MOSFETs with optimized source, drain and gate access, the degradation of the maximum oscillation frequency is mainly related to the increase of the parasitic feedback gate-to-drain capacitance and output conductance with the physical channel length reduction. Optimization of these internal parameters is needed to further improve the high frequency performance of ultra deep submicron MOSFETs. Index Terms—RF CMOS, RF SOI, silicon device characteriza- tion. I. INTRODUCTION L OW POWER, low voltage silicon-based technologies have recently been developed to produce highly integrated mixed mode circuits for wireless applications. Historically device scaling remains the primary method by which the semiconductor industry has improved productivity and perfor- mance. From the 100-nm technology node, upcoming CMOS technologies will have to face many grand technological challenges. In this context, the most critical issue consists in the so-called short-channel effects (SCE). These parasitic effects tend to degrade the subthreshold characteristic, increase the leakage current and lead to a dependence of threshold voltage with respect to the channel length. They have been reported theoretically and experimentally in the literature and solutions have been proposed. However, no result has been presented about the limitation or degradation of high frequency characteristics versus the downscaling of the channel length. Fig. 1 represents the state-of-the-art values of and for both silicon MOSFETs [1]–[9], [16] and III-V HEMTs [10]–[15] as function of the effective channel length. and are defined respectively as the transition frequency (i.e., the gain is equal to 0 dB) for Mason’s gain and for the current gain . The values of equivalent circuit parameters and transition frequencies of comparable effective channel length MOSFET (70 nm) and In/AlAs/InGaAs HEMT (75 nm) are summarized in Table I. The equivalent circuit data are Manuscript received November 20, 2002; revised January 14, 2003. This re- view of this letter was arranged by Editor B. Yu. G. Dambrine, M. Vanmackelberg, F. Danneville, and S. Lepilliet are with IEMN, F-59655 Villeneuve d’Ascq, France. C. Raynaud is with STMicroelectronics, F-38926 Crolles Cedex, France. D. Lederer, M. Dehan, and J.-P. Raskin are with the Université catholique de Louvain (UCL), B-1348 Louvain-la-Neuve, Belgium. O. Rozeaux is with CEA-LETI, F-38054 Grenoble Cedex 9, France. Digital Object Identifier 10.1109/LED.2003.809525 Fig. 1. State-of-the-art values of and and their ratio, for MOSFETs (silicon bulk and SOI technologies) and HEMT (InP & GaAs) versus the effective channel length ( physical gate length reduced by the overlap channel length which is assumed to be equal to 20 nm for the considered MOSFETs). extracted using methods described in [18] and [19], from 45 MHz to 50 GHz on-wafer measurements and the and values are obtained respectively by 20dB/dec. extrapolations of and gains calculated from measured parameters. Considering a classical small-signal equivalent circuit for MOSFET, we assume (1) with and with , the gate transcon- ductance, , the total gate-to-source input capacitance and , the total gate-to-drain capacitance. It should be added that physics-based simulations show that is very low and is strongly conditioned by the value of (in a regime of channel saturation) which depends on the source-drain-extension (SDE) process. Another important parameter of a microwave transistor is its intrinsic cutoff fre- quency determined by the ratio . It measures the intrinsic ability of a field effect transistor (FET) to amplify high frequency signals. The values are a factor of 2 to 2.5 higher for HEMTs than for comparable Silicon MOSFETs 0741-3106/03$17.00 © 2003 IEEE