PSP-based scalable compact FinFET model G.D.J. Smit 1 , A.J. Scholten 1 , G. Curatola 2 , R. van Langevelde 3 , G. Gildenblat 4 , and D.B.M. Klaassen 1 1 NXP Semiconductors Research, High Tech Campus 5, 5656 AE Eindhoven, The Netherlands — 2 NXP Semiconductors Research, Leuven 3 Philips Research Europe, Eindhoven, The Netherlands — 4 Arizona State University, Tempe AZ, USA (Invited) ABSTRACT A high-quality compact FinFET model is a prerequisite for initial circuit design and evaluation of these prospec- tive replacements for conventional bulk MOSFETs in real circuits. Our PSP-based compact model for symmetric 3-terminal FinFETs with thin undoped or lightly doped body contains simple analytical expressions for currents and charges. This makes the model well suited for such circuit simulations. Yet, this surface potential based model offers an accurate description of not only the currents, but also of the (trans-)conductance and capacitances and is continuous over all operating conditions (subthreshold, linear, satura- tion). The model is fully scalable and will be demonstrated to describe a full range of device geometries, from the long- channel limit down to the shortest channels, with a single set of parameters. Keywords: FinFET, compact model, PSP, CMOS, scaling 1 INTRODUCTION FinFETs are generally seen as prospective replacements for conventional bulk MOSFETs owing to their superior con- trol of short-channel effects (SCEs). They present, how- ever, a serious challenge for compact model development, e.g., due to the different electrostatics. Recently, we pre- sented a new surface potential based compact model for symmetric 3-terminal FinFETs with thin undoped or lightly doped body [1]. It is a complete compact model including SCEs, mobility reduction, and quantum mechanical (QM) corrections, based on well-established techniques from the PSP model [2],[3]. The model describes both currents and charges and is continuous over all operating conditions (sub- threshold, linear, saturation). The model has a hierarchical structure (similar to that of the PSP-model [2]), in which the above features are handled at the ‘local’ model level. An essential requirement of a com- pact model is its ability to give a description of device prop- erties as a continuous function of the device geometry. In case of FinFETs, the channel length L is usually the only de- sign parameter (the fin thickness and fin height are fixed by the technology). The L-scaling properties of the model are handled at the ‘global’ model level. In this paper, we will first give a description of the model core (that is, the core of the local model) in much more de- S D G G y x x = 0 t ox x = L y = t Si /2 y = −t Si /2 Figure 1: Schematic of device cross section (parallel to wafer), in- dicating dimensions, coordinate system, and terminal connections. tail than in [1]. In the second part, we will extend the work in [1] by focussing on the global model level and treating the scaling-behavior (channel length dependence) of the model. 2 MODEL CORE 2.1 Conventional approach We consider a symmetric FinFET with undoped (or lightly doped) body (see Fig. 1). Moreover, we consider a section from an infinitely high fin, i.e., edge-effects due to the top-gate and the buried oxide are neglected. We start by formulating the general theory along the same lines as, e.g., in [4]. Adopting the gradual channel approximation, the Poisson equation across the channel can be written as d 2 ψ dy 2 = exp(ψ − v) 2 , (1) where ψ(x, y) is the electrostatic potential and v(x) the quasi- Fermi level of the electrons (also known as the ‘channel po- tential’). It is convenient to express all voltages (such as ψ, v, and the terminal voltages) in units of ϕ T = k B T /e. Similarly, all lengths (such as x, y, L) are expressed in units of the Debye length L D =  ε Si ϕ T /(2eN A ), where N A is the equilibrium electron concentration 1 . 1 In the context of this paper, the value of N A used in the normalization can be chosen randomly, in principle. It is a matter of convenience to take N A equal to the intrinsic carrier concentration in an undoped fin, or to the doping level in a (lightly) doped fin. NSTI-Nanotech 2007, www.nsti.org, ISBN 1420061844 Vol. 3, 2007 520