![]() So, energy required for an electron to move from Fermi level to free space is called work function (qΦ S) and it is given by The potential difference between conduction band and free space is called electron affinity and is denoted by qx. Fermi potential Φ F is the difference between intrinsic Fermi level (E i) and Fermi level (E FP). Where Fermi level E F depends on the doping concentration. Here, Fermi potential Φ F is the difference between intrinsic Fermi level (E i) and Fermi level (E FP). Now, to understand the MOS structure, consider the energy level diagram of p–type silicon substrate.Īs shown in the figure, the band gap between conduction band and valance band is 1.1eV. Here, doping concentration N A is (10 15 to 10 16 cm −3) greater than intrinsic concentration ni. So, electron and hole concentration in p–type substrate is Now assume that substrate is equally doped with acceptor (Boron) concentration N A. N i is intrinsic carrier concentration of Silicon Now, to understand the structure of MOS, first consider the basic electric properties of P – Type semiconductor substrate.Ĭoncentration of carrier in semiconductor material is always following the Mass Action Law. Carrier concentration and distribution within the substrate can be manipulated by external voltage applied to gate and substrate terminal. The thickness of dielectric material (SiO 2) is usually between 10 nm and 50 nm. MOS structure forms a capacitor, with gate and substrate are as two plates and oxide layer as the dielectric material. Structure of a MOSFETĪs shown in the figure, MOS structure contains three layers − These transistors are formed as a ‘sandwich’ consisting of a semiconductor layer, usually a slice, or wafer, from a single crystal of silicon a layer of silicon dioxide (the oxide) and a layer of metal. CMOS offers low power dissipation, relatively high speed, high noise margins in both states, and will operate over a wide range of source and input voltages (provided the source voltage is fixed)įor the processes we will discuss, the type of transistor available is the Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). Today’s computers, CPUs and cell phones make use of CMOS due to several key advantages. Complementary MOSFET (CMOS) technology is widely used today to form circuits in numerous and varied applications.
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