Extended Abstracts of the 1999 International Conference on Solid State Devices and Materials, Tokyo, 1999, pp. 26-27 Simulation of Temperature Dependence of Microwave Noise in MOS Transistors Michael Obrecht* and Tajinder Manku RF Technology Group, Electrical and Computer Engineering Departrnent, University of Waterloo Waterloo, Ontario, N2L 3Gl Canada Phone: 519-888-4567 ext. 2082 Fax: 519-746-5195 e-mail: obrecht@siborg.ca 1. Introduction 2D fransient device simulation was used to evaluate temperature dependence of the microwave noise in MOS ffansistors. The method had proven to predict realistically noise parameters of MOS transistors. Results for a 0.5 pm LDD NMOS ffansistor are presented. The results show strong temperature effect on the noise that is not described by existing models. Improved characteristics of sub-micron MOS transistors (see e.g. tll) made CMOS a viable RF technology for porrable wireless systems. For RF circuits, low noise design is one of the key issues. Unavailability of a good MOSFET high frequency noise model in commonly used circuit simulators makes RF circuit design very difficult. A limited amount of information on this subject is published and it is primarily experimental data 12,31. A two-dimensional device simulation is usually used to predict characteristics of short channel MOSFETs. Recently it has been demonsfated that two-dimensional noise simulation can be successfully used to predict noise in practical semiconductor devices t4-61. It has also been shown [5,6] that conventional expression for the channel noise fails.for short channel MOSfiETs indicating that the nature of carrier transport changes for short channel MOSFETs. To further investigate possible causes of this change and possibly to characterize the main cause it seems appropriate to vary other parameters affecting the noise, for example the temperature. Besides, this study would also have a practical application such as design issues for equipment operating in extreme conditions, for example onboard an aircraft. In this paper, we use transient 2-D device simulation to characterize the microwave noise performance of a MOSIIET at temperatures ranging from 200 to 400 degrees Kelvin. The method allows not only to calculate the device noise perforrirance but also to visualize an internal noise sources inside the device. Therefore, the method can be used to optimize the device structure/process for better noise performance. A-2-4 2. Simulation Method The 2-D noise simulation has been implemented into the framework of the device simulator developed by Siborg Systems Inc. The noise specfra are obtained using a method similar to the Impedance Field Method (see e.g. [4]). In ur*is procedure, a noise current is injected at each grid point within a 2-D device structure and the terminal currents are recorded as a function of the position in which they were injected. For each injected source, the induced noise current at the terminals can be obtained using, where i" (t) is the induced noise current at the terminal or, s(rrt) is the electron injection rate caused by the noise at the location r, C) is the domain of the device, and Go(V,t,tr) is the current transfer function. This function represents the fraction of current emerging through terminal or due to the injected current at position r. This interpretation of the function Go(f,t,tr) becomes clear when we apply a Fourier transformation to (1), obtaining, i"(@) - Ic"(7,ar)s(F, @)ffi (2) where we have assumed a stationary condition. From this interpretation, it clear that Gois closely related to the Green's function (Impedance Field) defined in [4]. After G"(f ,a) is constructed, the power spectrum density and the noise correlation are determined using, <;";i >=JV ico(f,a).Rg,ot1.vrci(f ,a)dt (3) where k(t,a) = qq'be)n(n and bff1 is the diffrrsivity tensor, n(F) is the electron density at the DC operating point. I io(t1 - IIo,fr,t,tr)s(i,t)dfdtt (1) -6o *also with Siborg Systems lnc, www.siborg.ca 26