MOSFET depletion

This circuit is an NMOS inverter with a depletion load. Many textbooks describe MOSFET operation by the following equations ... 

We are calling the new model My. Note that the symbols for enhancement- and depletion-mode MOSFETs are the same. PSpice knows that a MOSFET is either an enhancement- or a depletion-mode MOSFET by the value of the threshold voltage parameter, VtO. 

Metal oxide semiconductor field-effect transistors (MOSFETs) are field effect transistors with a thin film of silicon dioxide between the gate electrode and the semiconductor. The charge on the silicon dioxide controls the size of the depletion zone in the polype semiconductor. MOSFETs are easier to mass produce and are used in integrated circuits and microprocessors for computers and in amplifiers for cassette players. Traditionally, transistors have been silicon based but a recent development is field-effect transistors based on organic materials. 

After the MOSFET turns off, the drain voltage rises and the primary peak current is delivered to the load. The current then falls at a rate determined by the output voltage and the primary inductance. Once the energy in the primary inductance is depleted, the drain voltage falls, in accordance with the resonant characteristics of the primary inductance and the resonant capacitance (plus the primary transformer capacitance and the MOSFET output capacitance). 

Although the two choices each of type (JFET, MOSFET) of channel (n-channel, p-channel) and doping (enhancement, depletion) could yield eight choices, in practice only five main FET types exist ... 

MOSFETs is always positive, e and are the dielectric constant and thickness of Si02 respectively, (z) is the distribution of electron concentration along z direction for a given x-coordinate in the channel, is the acceptor concentration in the depletion region, z pi is the depth of the... 

The first SiC MOSFETs were fabricated by Suzuki et al [1] in 3C-SiC. At the present time, SiC MOSFET research is carried out by several groups, including Cree Research [2-4] and Westinghouse [5]. Enhancement mode and depletion mode (3-SiC MOSFETs have been fabricated by Palmour et al [3]. Enhancement mode devices with 5 pm gate lengths had a maximum transconductance (gm) of 0.46 mS mm 1 at room temperature (see FIGURES 1 and 2). The devices were operational up to 823 K. 

The depletion mode 6H-SiC MOSFETs fabricated by the General Electric group [8] exhibited a fairly low leakage current of 5 x 10 " A at 23 °C at -10 V gate bias and drain bias of 8 V with the on-current as high as 1.6 mA. However, the subthreshold was quite low. These devices operated up to 350 °C. 

FIGURE 5 Cross-section of a depletion mode n-channel (3-SiC MOSFET [3],... 

FIGURE 7 Current-voltage characteristics of a depletion mode n-channel a-SiC MOSFET [7]. 

Analogous to these field-effect devices is the buried-channel, depletion-mode, or normally on MOSFET, which contains a surface layer of the same doping type as the source and drain (opposite type to the semiconductor body of the device). As a result, it has a built-in or normally on channel from source to drain with a conductance that is reduced when the gate depletes the majority carriers. 

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