Contents I. Introduction
Accurate analytical models of MOS device current are very important for circuit analysis and for projecting the performance of CMOS to future nanoscale device dimensions. Our understanding of MOS device physics has greatly improved over the past several decades. However, not all this improved understanding has been incorporated into MOS device models. The basic “quadratic” MOS current expression developed in the early 1960s [1]–[3] can be expressed below the current saturation region byI_{d}=\mu_{n}C_{\rm ox}\left({W\over L}\right)(V_{g}-V_{T}-{0.5}V_{d})V_{d}.\eqno{\hbox{(1)}}This basic model has been recognized as inadequate for many years and various modifications have been made to this basic starting equation. One of the most common is to modify the mobility so that it becomes a function of the form\mu_{n}={\mu_{o}\over\left[1+\theta_{1}(V_{g}-V_{T})+\theta_{2}(V_{g}-V_{T})^{2}\right]\left[1+{V_{d}\over E_{c}L}\right]}\eqno{\hbox{(2)}}where the first term in square brackets in the denominator is intended to account for the known reduction in mobility due to the vertical gate oxide field and the second term in square brackets is intended to account for velocity saturation effects due to a large horizontal drain field. An extensive literature exists describing various modifications to the basic MOS current equation.
