Presentation on theme: "Power FET Structure DMOS and VMOS"— Presentation transcript:
1 Power FET Structure DMOS and VMOS AbstractPower MOSFETS are designed to handle significant power levels. It’smain advantages are its high commutation speed and good efficientat low levels. Power MOSFETS have different structures than lateralMOSFETS by having a vertical structure rather than a planarstructure. The DMOS and VMOS both exhibit a vertical structure thatwill be discussed.By: John Fox, Jake French4/25/14
2 Outline DMOS What is is? Where is it used? DMOS Structure VMOS VMOS Structure
3 DMOS Double diffused metal oxide semiconductor Most Power MOSFETs are made using this technologyUsed in switching applications with high voltage and high frequency behaviorTypically used in:Automobile control electronicsInkjet printheadsPower supplies
4 DMOS Structure The DMOS device incorporates a double diffusion process The p-substrate region and the n+ source contact are diffused through a common window defined by the edge of the gateThe p-substrate region is diffused deeper than the n+ sourceThe surface channel length is defined as the lateral diffusion distance between the p-substrate and the n+ source
5 DMOS StructureElectrons enter the source terminal and flow laterally through the inversion layer under the gate to the n-drift regionThe electrons then flow vertically through the n-drift region to the drain terminalThe conventional current direction is from the drain to the source
6 DMOS StructureCross-section of a double-diffused MOS (DMOS) transistorSemiconductor Physics and Devices Textbook by Donald A. Neamen
7 DMOS StructureMost important characteristics are the breakdown voltage and on-resistanceThe increase in resistance with temperature provides stability for the power MOSFETDMOS is similar to a BJT, they share high-voltage and high-frequency characteristics
8 DMOS StructureA lightly doped drift region between the drain contact and the channel region helps ensure a very high breakdown voltageThe n-drift region must be moderately doped so that the drain breakdown voltage is sufficiently largeThe thickness of the n-drift region should be as thin as possible to minimize drain resistance
9 VMOSV-groove MOSFET - a power MOSFET in which the channel region is formed along a v-shape d groove formed in the surface of the semiconductorThis MOSFET gets its name from the “V” shape groove that is formed after the p-substrate diffusion is performed over the entire surface followed by the n+ source diffusion
10 VMOSVMOS power devices are used in medium voltage power supply switching applications and medium power RF amplifiersTypically used in:Hi-fi audio power amplifiersBroadband high-frequency amplifiersSwitching power amplifiers which convert AC power sources in DC at arbitrary voltages
11 VMOS Cross-section of a Vertical channel MOS (VMOS) transistor Semiconductor Physics and Devices Textbook by Donald A. Neamen
12 VMOS StructureThe V-groove is easily fabricated by anisotropically etching a (100) silicon surface using a concentrated KOH solution.V shaped gate region increases the cross-sectional area of the source-drain path.This reduces the on resistance of the device allowing it to handle high voltages
13 VMOS StructureThe gate consists of a metallised area over the V groove and this controls the current flow in the P region.As the gate is fabricated in this way it means that the device retains the exceptionally high input resistance typical of the MOS family of devices.
14 VMOS StructureCurrent flows horizontally between the source and drain, controlled by the potential on the gate.As the current only flows through a relatively small area, resistance values can be high reducing the efficiency of the device.One of the main drawbacks of the VMOS power device is that the structure is more complicated than a traditional FET and this makes it slightly more expensive.
15 Summary Power MOSFETS differ from lateral MOSFETS with the vertical structure of the DMOS and the VMOS. These areused in a variety of applications that desire high switchingspeeds and a variety of voltage levels. The doping andchannel lengths contribute to the characteristics of eachof these MOSFETS.
16 ReferencesPoole, Ian. "VMOS Field Effect Transistor." :: Radio-Electronics.Com. N.p., n.d. Web. 22 Apr"V-Groove MOS (VMOS)." Electronic Circuits and DiagramElectronics Projects and Design RSS. N.p., 4 Aug Web. 22 Apr"Double-Diffused MOS (DMOS)." Electronic Circuits and DiagramElectronics Projects and Design RSS. N.p., 28 July Web. 22 Apr"Double-diffused MOS (DMOS) Technology | JEDEC." Dictionary Entries. N.p., n.d. Web. 22 AprVan Zeghbroeck, Bart. "Chapter 7: MOS Field-Effect-Transistors." Power MOSFETs. N.p., Web. 22 AprNeamen, Donald A. "15.5 Power MOSFETs." Semiconductor Physics and Devices: Basic Principles. New York, NY: McGraw-Hill, N. pag. Print.
17 Key PointsA power MOSFET has a vertical configuration and an interdigitated gate-source surface structureDMOS uses a double diffusion processMost important characteristics are the breakdown voltage and the on-resistance.V shaped gate increases the cross-sectional area of the source-drain path.The main advantages are the high commutation speed and its good effiency at low voltages.