MOSFET Performance Improvement: Decision Factors of RDS(ON)

(1) The MOSFET device structure is selected according to the required voltage rating(VDSS). For example, many middle and high voltage MOSFETs (VDSS=250V or higher) have planar gate MOS(π-MOS) structure, and products with less than VDSS=200V have more trench gate MOS(U-MOS).
(2) The factor that determine the on-resistance RDS(ON) are shown in Fig.3-7 and Equation 3-(1). Depending on the structure and VDSS of MOSFET, the ratio of factors determining RDS(ON) will change. When the  π-MOS structure is chosen, Rdrift becomes the dominant factor in VDSS=600V products, while the ratio of Rch+RJ-FET is high in VDSS=30V products. However by applying U-MOS structure, Rch will be very small.

RDS(ON)=Rsub+Rdrift+RJ-FET+Rch+RN+  --- Equ.3-(1)a

RDS(ON)= Rsub+Rdrift+Rch+RN+    --- Equ.3-(1)b

@ VDSS=600 V :  Rdrift >> Rch > RJ-FET , RN+ , Rsub    RDS(ON) depends on Rdrift
@ VDSS=  30V  :  ●π-MOS --- Rch + RJ-FET > Rdrift >> RN+ , Rsub.     ●U-MOS --- Rch≈ Rdrift >> Rsub, RN+

                              Dependence of RDS(ON) on Rch can be minimized by fine patterning of U-MOS structure.

Chapter III : Transistors

Types of Transistors
Bipolar Transistors (BJTs)
Bias Resistor Built-in Transistors (BRTs)
Junction Field-Effect Transistors (JFETs)
Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)
Differences between BJT and MOSFET
Structure and Operation of MOSFET
MOSFET Performance Improvement: Approach to Low RDS(ON)
MOSFET Performance Improvement: Super-Junction MOSFETs (SJ-MOS)
Summary of MOSFET Features by Structure
Performance of MOSFETs: Drain Current and Power Dissipation
Performance of MOSFETs: Avalanche Capability
Performance of MOSFETs: Characteristic of Capacitance
Performance of MOSFETs: Safe Operating Area(or Area of Safe Operation)
Insulated-Gate Bipolar Transistors (IGBTs)
Operation of Insulated-Gate Bipolar Transistors (IGBTs)
Performance Improvement of IGBTs: Evolution of Vertical Design
What are RC-IGBTs and IEGTs?
Application of IGBTs
Comparison of Forward Characteristics of IGBTs and MOSFETs
Comparison of Transistors by Structure
Datasheets of MOSFET: Maximum Ratings
Datasheets of MOSFET: Electrical Characteristics
Datasheets of MOSFET: Capacitance and Switching Characteristics
Datasheets of MOSFET: Body Diode

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