Physics
MOSFET Switch
A MOSFET switch is a type of transistor that can be used to control the flow of electrical current in a circuit. It operates by applying a voltage to the gate terminal, which in turn modulates the conductivity between the source and drain terminals. This allows the MOSFET to act as an electronic switch, turning the current on or off as needed.
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10 Key excerpts on "MOSFET Switch"
- Mike Golio, Janet Golio, Mike Golio, Janet Golio(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
18 Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) Julio Costa Mike Carroll G. Ali Rezvani Tom McKay RF Micro Devices 18.1 Introduction .............................................. 18 -2 18.2 A Brief History of the MOSFET ........................ 18 -3 18.3 Moore’s Law .............................................. 18 -5 18.4 The Metal-Oxide-Semiconductor Interface ............ 18 -6 Donors and Acceptors • The MOS Surface Charge Q s and Surface Potential ψ s • The Capacitance–Voltage Characteristics of the MOS Stack 18.5 The 1-Dimensional Long-Channel MOSFET I–V Model ................................................ 18 -13 The MOSFET Threshold Voltage V TH 18.6 The Long-Channel MOSFET Current–Voltage Model ..................................................... 18 -14 The Subthreshold Region • Short-Channel Effects in Modern MOSFETs 18.7 MOSFET Fabrication Section ........................... 18 -19 Introduction to MOSFET Fabrication • Example CMOS Device Cross Section • Example CMOS Layout • Modern RFCMOS Front-End Process Flow • CMOS Back-End Process Flow • MIM Capacitors • Resistors • Silicon on Insulator Processes References ....................................................... 18 -40 18 -1 18 -2 RF and Microwave Passive and Active Technologies 18.1 Introduction The Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is today the most utilized electronic semiconductor device in the world, covering a vast range of electronic applications. Its usage ranges from simple single transistor designs to complex high-speed very large-scale integration (VLSI) cir-cuits containing tens of millions of transistors, integrated on the same monolithic silicon die, covering a wide range of analog and digital applications.
eBook - PDF- Stefan Linder(Author)
- 2006(Publication Date)
- EPFL PRESS(Publisher)
The MOSFET is a four terminal device: the power terminals are the drain and the source. The current path between the drain and source is opened and closed via a control terminal, which is referred to as the gate. Also the substrate of the device 184 The Power MOSFET must be electrically connected to the circuit. This connection is established via the body contact. The name MOS refers to the sequence of materials along the cross-section A-A', as shown in Figure 7.1. The top layer is the Metal (MOS) 1 . Below the metal, there is an insulator, also referred to as the gate oxide. This name indicates that the insulator is normally an Oxide (MOS). The most widely employed oxide is SiO 2 ; however, it is also possible to use other insulators, such as silicon nitride (Si 3 N 4 ). The bottommost material in the cross-section is the Semiconductor (MOS), which is usually silicon. Besides silicon, many other semiconductor materials are in use, such as GaAs (gallium arsenide), GaN (gallium nitride), and SiC (silicon carbide). The structure along the line A-A' is referred to as a MOS interface. Figure 7.2 shows its band diagram, with the assumption that the gate and the body are short-circuited, i.e., V GB = 0. Under these conditions, no energy can be transported between the gate and the body. Hence, the Fermi energy E F is at the same level on both sides of the MOS interface. The energy, which must be invested to transport an electron from the Fermi level of the metal to the vacuum, is referred to as the work function of the metal; it is denoted as , illustrated in Figure 7.2. Analogous to this, is the work 1 It should be mentioned here that the expression MOS dates from the time when only metal gates were employed for MOS transistors. In modern MOSFET technologies, metal has been almost completely replaced by heavily doped polysilicon or by sintered metal-polysilicon alloys (referred to as silicides).
eBook - PDFPower Microelectronics
Device and Process Technologies
- Yung C Liang, Ganesh S Samudra;;;(Authors)
- 2009(Publication Date)
- WSPC(Publisher)
POWER METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR 4.1. Introduction The operational principle of the metal-oxide-semiconductor field-effect tran-sistor (MOSFET, or sometimes called MOS in short) devices originates from the field-effect concept by Lilienfeld in the 1930s. When the industry even-tually learned how to grow the good-quality gate dielectric with acceptable charges, the n-MOS technology and the later CMOS technology took off in a fast path. Today, MOS device technology, namely CMOS or BiCMOS pro-cess, becomes prevalent and dominant in integrated circuit (IC) development. At the same time, power MOSFET devices began to emerge and were intro-duced in 1970s. So far, many structures for power MOSFET devices have been proposed, such as the double-diffusion MOSFET (or DMOS), V-groove MOSFET (or VMOS), and trenched-gate UMOS. Due to many processing difficulties related to the gate dielectrics and the enhanced electric field at the tip of the V-groove (Holmes and Salama, 1973), the VMOS structure is seldom used in production. Instead, the DMOS structure is a preferred choice. For the UMOS structure, it is seen as the preferred choice to provide a low on-state resistance. The introduction of power MOSFET brought about the prediction of the extinction of the bipolar power transistor. However, this prediction did not happen immediately as cost and reliability plagued the power MOSFET. The bipolar power transistor continued to be used in many high-voltage and high-current applications. Only in the mid-1980s, the bipolar power transistor finally met the most critical rival with the introduction of the insulated-gate bipolar transistor (IGBT), which will be described in Chapter 5. 141 142 Power Microelectronics The high gate impedance is a primary feature of the power MOSFET that greatly simplifies its gate-drive circuitry. The negative temperature coefficient of the drain current, i.e.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- University Publications(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 9 MOSFET Two power MOSFETs in the surface-mount package D2PAK . Operating as switches, each of these components can sustain a blocking voltage of 120 volts in the OFF state, and can conduct a continuous current of 30 amperes in the ON state, dissip ating up to about 100 watts and controlling a load of over 2000 watts. A matchstick is pictured for scale. ____________________ WORLD TECHNOLOGIES ____________________ A cross section through an nMOSFET when the gate voltage V GS is below the threshold for making a conductive channel; there is little or no conduction between the terminals source and drain; the switch is off. When the gate is more positive, it attracts electrons, inducing an n -type conductive channel in the substrate below the oxide, which allows electrons to flow between the n -doped terminals; the switch is on. Result for formation of inversion channel (electron density) and attainment of threshold voltage (IV) in a nanowire MOSFET. Note that the threshold voltage for this device lies around 0.45V. The metal–oxide–semiconductor field-effect transistor ( MOSFET , MOS-FET , or MOS FET ) is a device used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first proposed by Julius Edgar Lilienfeld in 1925. In MOSFETs, a voltage on the oxide -insulated gate electrode can induce a conducting channel between the two other contacts called source and drain. The channel can be of n-type or p-type , and is accordingly called an nMOSFET or a pMOSFET (also commonly nMOS, pMOS). It is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common. The 'metal' in the name is now often a misnomer because the previously metal gate material is now often a layer of polysilicon (polycrystalline silicon).
eBook - PDF- Behzad Razavi(Author)
- 2021(Publication Date)
- Wiley(Publisher)
MOSFETs are electronic devices that can operate as voltage-dependent current sources. • A MOSFET consists of a conductive plate (the “gate”) atop a semiconductor sub- strate and two junctions (“source” and “drain”) in the substrate. The gate controls the current flow from the source to the drain. The gate draws nearly zero current because an insulating layer separates it from the substrate. • As the gate voltage rises, a depletion region is formed in the substrate under the gate area. Beyond a certain gate-source voltage (the “threshold voltage”), mobile carriers are attracted to the oxide-silicon interface and a channel is formed. • If the drain-source voltage is small, the device operates a voltage-dependent resistor. Problems 301 • As the drain voltage rises, the charge density near the drain falls. If the drain voltage reaches one threshold below the gate voltage, the channel ceases to exist near the drain, leading to “pinch-off.” • MOSFETs operate in the “triode” region if the drain voltage is more than one thresh- old below the gate voltage. In this region, the drain current is a function of V GS and V DS . The current is also proportional to the device aspect ratio, W∕L. • MOSFETs enter the “saturation region” if channel pinch-off occurs, i.e., the drain voltage is less than one threshold below the gate voltage. In this region, the drain current is proportional to (V GS − V TH ) 2 . • MOSFETs operating in the saturation region behave as current sources and find wide application in microelectronic circuits. • As the drain voltage exceeds V GS − V TH and pinch-off occurs, the drain end of the channel begins to move toward the source, reducing the effective length of the device. Called “channel-length modulation,” this effect leads to variation of drain current in the saturation region.
eBook - PDFSilicon, From Sand to Chips, Volume 1
Microelectronic Components
- Alain Vignes(Author)
- 2024(Publication Date)
- Wiley-ISTE(Publisher)
6 The MOSFET Transistor Research on the effect of an electric field on the conductivity of a doped semiconductor wafer, by William Shockley as early as 1945, led to the demonstration of a direct field effect as early as 1947 by John Bardeen and Walter (see Chapter 3, section 3.1.2.2). But due to the problem of “surface states” (traps), it was not until 1959 that the first silicon MOSFET was produced by Martin Atalla and Dawon Kahng of Bell Labs. It was the qualities of silicon oxide that led to the development of the silicon-based MOSFET transistors. The first commercial transistors appeared in 1964. The MOSFET transistor became the preferred component for computer logic circuits and memories in 1970, because of its low power consumption and miniaturization capacity. Miniaturization by a factor of 1,000 has been achieved in 50 years, which means a reduction in the switching time by a factor of 1,000 and therefore an increase in operation speed. The miniaturization of transistors has posed acute problems in terms of manufacturing processes, dielectric and electrode materials for the gate, source and drain, and electrical connections. This chapter presents: – the transistor operation (in static regime); 176 Silicon, From Sand to Chips 1 – the functions: switching and amplification; – the CMOS component; – the development history of the MOSFET transistor; – the evolution of MOSFET transistor materials imposed by miniaturization (Moore’s law). 6.1. Features and functions 6.1.1. Introduction The field effect (presented in Chapter 3, section 3.1.1) consists of the polarization (conductivity inversion and/or modulation) of a thin surface layer of a wafer or thin film of a doped semiconductor, induced by the application of an electrostatic field perpendicular to the semiconductor surface via a flat electrode close to and parallel to the wafer surface.
eBook - PDFElectronic Concepts
An Introduction
- Jerrold H. Krenz(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
Junction field-effect transistors are utilized both as discrete devices and, most frequently, in conjunction with bipolar junction transistors in integrated circuits. It is a more recent development, however, that of the metal-oxide semiconduc-tor field-effect transistor (MOSFET), that has had perhaps the most profound effect on the design of electronic systems. This transistor was first proposed by Kahng in 1960 (Kahng 1976), and its theory of operation was published 3 years later (Hofstein and Heiman 1963). Very-large-scale integrated circuits rely on this device, which is, structurally, considerably simpler than the bipolar junc-tion transistor. In addition, MOSFET devices require fewer processing steps and can be made considerably smaller than bipolar junction transistors. As a result, 217 source drain SiO 2 p-type substrate substrate Figure 4.1: Metal-oxide field-effect transistor. extremely high device (and therefore logic) densities can be achieved (Hittinger 1973). The basic structure of a MOSFET device with a p-type substrate is illustrated in Figure 4.1. This device has two heavily doped w-type semiconductor wells, labeled source and drain, embedded in the p-type substrate. A metallic gate extends between the wells and is insulated from the substrate by a thin silicon dioxide layer. Because silicon dioxide is a dielectric, the gate and substrate form a capacitor in which a gate-to-substrate potential results in induced surface charges at the boundary of the dielectric and the substrate. To gain an appreciation of the operation of this device, suppose that the gate is floating (no connection) and that it has no residual charge. An equivalent circuit consisting of two junction diodes applies (Figure 4.2). For no connection to the substrate, the current between the source and drain will be negligible regardless of the polarity of an externally applied voltage difference (one diode will be reverse biased).
eBook - PDFFundamentals of Electronics
Book 1 Electronic Devices and Circuit Applications
- Thomas F. Schubert, Ernest M. Kim(Authors)
- 2022(Publication Date)
- Springer(Publisher)
To insure proper operation of the devices, manufacturers’ specifications on maximum voltages must be heeded. Due to the JFET fabrication process, the drain and source can, in most cases, be inter- changed when the JFET is used as a circuit element without affecting the desired operating char- acteristics. is property (drain-source reciprocity) is not common to all types of FETs. e characteristics of the FETs in the different regions are shown in Table 4.2. %SBJO4PVSDF 1PUFOUJBM %SBJO4PVSDF $IBSHF 'MPX $VU0 $VU0 FYDFQU +'&5T $VU0 4BUVSBUJPO 0INJD #SFBLEPXO Figure 4.37: FET regions of operation. 4.5 THE FET AS AN ANALOG SWITCH Both Bipolar Junction and Field Effect Transistors can be used as switches in a wide variety of analog electronic applications. Each type provides a great advantage over mechanical switches in both speed, reliability, and resistance to deterioration. FETs are the more common choice due to the inherent symmetry of FETs and the undesirable offset voltage (V CE at I C D 0) that 266 4. FIELD EFFECT TRANSISTOR CHARACTERISTICS is present in BJTs. e offset voltage of BJTs, typically on the order of a few millivolts, can produce significant errors in the transmission of low-level analog signals. Another advantage of FET switches is the high gate input impedance and the consequent low load that the voltage control port presents to control electronics. Among the many possible electronic applications of solid-state analog switches are the following: • Sample-and-hold circuits • switchable gain amplifiers • switched-capacitor filters • digital-to-analog conversion • signal gating and squelch control • chopper stabilization of amplifiers In addition, multiple switches connected to share a common output form a multiplexer: a common building block for analog and digital systems. e basic function of a switch is to electrically isolate or connect two sections of a circuit.
eBook - ePubFundamentals of Silicon Carbide Technology
Growth, Characterization, Devices and Applications
- Tsunenobu Kimoto, James A. Cooper(Authors)
- 2014(Publication Date)
- Wiley-IEEE Press(Publisher)
The CO escapes as a gas, while the forms a native passivation layer on the SiC. SiC is the only wide bandgap semiconductor whose native oxide is, and this makes it possible to form the entire range of metal-oxide-semiconductor (MOS)-based devices in SiC. In this section we consider the simplest MOS-based power device, the power MOSFET. In Section 9.2 we will discuss another MOS-based power device, the insulated-gate bipolar transistor (IGBT). 8.2.1 Review of MOS Electrostatics To begin our discussion of SiC MOSFETs, we will first review the concepts of MOS electrostatics. Since MOS electrostatics are covered in many semiconductor textbooks, we will simply present the outline here and refer the reader to the literature for detailed derivations. We initially assume an ideal MOS structure with no charges in the, no interface states or fixed charges at the oxide/semiconductor interface, and zero metal-semiconductor work function difference. Figure 8.10 shows energy band and block charge diagrams for an ideal MOS capacitor on p-type SiC at three bias points: flat band, depletion, and inversion. We define an -coordinate system with the origin at the oxide/semiconductor interface and positive into the semiconductor. The oxide thickness is and the gate is assumed to be metal, with work function. The semiconductor substrate at is taken as our ground reference. Figure 8.10 Band diagrams of a p-type MOS capacitor biased (a) at flat band, (b) in depletion, and (c) in inversion. In the delta-depletion approximation, the inversion charge is a sheet charge (delta function) at, and the surface potential is defined on the semiconductor side of. For future analyses, we now define two important parameters of the MOS structure. The Fermi potential is the potential difference between midgap and the Fermi level far from the surface, as indicated in Figure 8.10. is determined by doping and temperature, and is given by 8.21 where is the ionized dopant concentration
eBook - PDF- Marian K. Kazimierczuk(Author)
- 2015(Publication Date)
- Wiley(Publisher)
Only a drift current flows through the device during the on-state conduction. The positive gate-to-source voltage v GS in an n-channel MOSFET repels the majority carrier holes and attracts the minority carrier electrons. For v GS > V t , the p-type region is inverted into n-type region, forming an n-channel between the drain and the source. The conducting n-channel is formed in a MOSFET when v GS > V t is applied and the electron density exceeds the hole density below the gate and the p-type semiconductor is inverted into the n-type inversion layer, connecting the drain to the source. The application of v GS above V t causes a build-up of free electrons in the inversion layer in direct proportion to the excess of v GS above V t . The enhancement-mode MOSFET is a normally-off device. The MOSFET threshold voltage V t can be reduced by reducing the oxide thickness t ox and the p-well doping concentration N A because V t is proportional to t ox and √ N A . The conductivity of the MOSFET channel is controlled by the gate-to-source voltage v GS applied across the metal–oxide–semiconductor (MOS) capacitor. When the drain-to-source voltage v DS increases at a fixed gate-to-source voltage v GS , the drain current i D initially increases, and then it saturates once the channel is pinched off near the drain end. The mobility of current carriers is the ratio of the average drift velocity to the applied electric field intensity, n = E∕v n . The silicon hole mobility is about one-third of the silicon electron mobility. The charge carrier mobility in the MOSFET channel is lower than that in the semiconductor bulk because of channel surface roughness scattering. A MOSFET channel should be wide and short to conduct large drain current. The mobility of electrons decreases as the doping concentration, temperature, and electric field increase.
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