Nikolaos Makris

Charge-Based Compact Model for Bias-Dependent Variability of 1/

Variability of low frequency noise (LFN) in MOSFETs is bias-dependent. Moderate-to-large-sized transistors commonly used in analog/RF applications show 1/f-like noise spectra, resulting from the superposition of random telegraph noise. Carrier number and mobility fluctuations are considered as the main causes of LFN. While their effect on the bias-dependence of LFN has been well investigated, the way these noise mechanisms contribute to the bias-dependence of variability of LFN has been less well understood. LFN variability has been shown to be maximized in weak inversion (subthreshold), while increased drain bias also increases LFN variability. However, no compact model has been proposed to explain this bias-dependence in detail. In combination with the charge-based formulation of LFN, this paper proposes a new model for bias-dependence of LFN variability. Comparison with experimental data from moderately sized nMOS and pMOS transistors at all bias conditions provides insight into how carrier number and mobility fluctuation mechanisms impact the bias-dependence of LFN variability.

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Purely vertical 4H-SiC JFETs have been modeled by using three different approaches: the analytical model, the finite element model and the compact model. The results of the modeling have been compared with experimental results on a series of fabricated self-aligned devices with two different channel lengths (0.3 and 1.1μm) and various channel widths (1.5, 2, 2.5, 3, 4 and 5 μm). For all the considered models I-V and C-V characteristics could be satisfactorily simulated.

Noise in MOSFETs

Variability of Low Frequency Noise (LFN) and Random Telegraph Noise (RTN) is an important concern for many analog CMOS integrated circuits. In this paper, transistors with enclosed gate layout are examined and compared with standard layout transistors, with particular emphasis on weak inversion region. Enclosed gate transistors show an improved gate voltage mismatch in weak inversion. A compact MOSFET model for LFN and its variability, based on number fluctuation theory, is shown to cover well the behavior of either type of transistors. Lower levels of noise as well as lower variability of noise are observed in enclosed gate transistors.

Modelling of 4H-SiC VJFETs with Self-Aligned Contacts

This paper presents and discusses the depletion mechanisms that dominate in a TSI-VJFET under different bias conditions as expressed by the gate-source (CGS) and gate-drain (CGD) capacitances. It is shown that at pinch off the dominant capacitance is the drift capacitance and that in conduction the drain source voltage plays a significant role in channel’s formation. Furthermore a semi empirical capacitance model is introduced. CGS and CGD are modeled below and above threshold voltage by considering parallel plate capacitors with different plate configuration in te two cases. Then, the derived expressions are unified using a transition function that preserves the continuity of the model. The model was adjusted and fitted adequately to measured CV data from fabricated TSI-VJFET.

Variability of Low Frequency Noise and mismatch in enclosed-gate and standard nMOSFETs

Different methods for cross-section characterization of SiC Trenched-singly-implanted vertical junction field effect transistors (TSI-VJFETs) are presented with the purpose to determine the epitaxial structure in terms of doping topography.