Transcript MOSFET

MOSFET
Author : Leslie LEONG
Transistor
STMicroelectronics
Session Objectives
By the end of this session, you will be able to :
–
Describe the basic Definition, Function, and Operation of MOSFETs.
–
Extract Key Parameters from MOSFETs Datasheet with ease.
–
Interpret the Nomenclature of MOSFETs.
–
Identify and Understand the core Applications of MOSFETs.
–
Trace the Evolution of ST MOSFETs in term of Technology, Packaging,
Application.
–
Distinguish the differences & uses of MOSFETs and Bipolars.
What is MOSFET?
MOSFET
STMicroelectronics
What is MOSFET ?
Definition

A MOSFET is a three-terminal devices which in basic term behaves
as a voltage controlled switch.
Drain
Gate
Source
Circuit Symbol
Source
Drain
Gate
Package Pin Layout
What is MOSFET ?
MOSFET : Metal - Oxide - Semiconductor
Field Effect Transistor
Metal Layer
: which forms the Gate (replaced by polysilicon).
Oxide Isolation Layer : which prevents current flow between the Gate and the other two electrodes
(Drain,Source) of the device, but does not block the electric field.
Semiconductor Layer : which depending on the voltage at the gate, either blocks or allow current to flow
between the Source and Drain contacts.
source contact
source
metal
intermediate dielectric
polysilicon gate
n+
p+
collector
current
n+
n+
p+
n- epy
n+ buffer layer
p+ substrate
Drain Back Metal
Basic Structure
Package Frame
Basic Functions
MOSFET
STMicroelectronics
Basic Functions

Basic Function : The devices allows conduction between the
Drain and Source terminals only if an
appropriate voltage is applied to the Gate.
Vdd
Load
D
Driver
G
S
Basic Theory of Operation
MOSFET
STMicroelectronics
Basic Theory of Operation
Output Characteristics
VDS = VGS - Vth
Output Characteristic
In the Linear region, the voltage across the channel is
not sufficient for the carriers to reach max current
density. The RDS(on) = VDS / IDS As VDS is increased, the
carriers reach their max drift velocity, the current
amplitude cannot increase, this is the so called
Saturation region.
source contact
source
metal
intermediate dielectric
polysilicon gate
n+
p+
collector
current
n+
n+
p+
n- epy
n+ buffer layer
p+ substrate
Drain Back Metal
Basic Theory of Operation
Transfer Characteristics
IDS
VGS
VTH
Key Parameters
MOSFET
STMicroelectronics
Key Parameters
MOSFETs can be selected based on :

V(BR)DSS (Drain-Source Breakdown Voltage)

RDS(ON) (Static Drain-Source On Resistance)

Qg (Total Gate Charge)

VGS(th) (Gate Threshold Voltage)

Package
Key Parameter
V(BR)DSS

This represents the lower limit of the devices blocking voltage capability from
Drain-to-Source with the Gate shorted to the Source. It is measured at a
specific leakage current (250uA), and has a positive temperature coefficient.
Normalised V(BR)DSS
1.15
1.10
D
1.05
G
Id = 250uA
S
1.00
0.95
0.90
0
-50
-25
0
25
50
75
100
Junction Temperature [ºC]
125
150
Key Parameter
RDS(ON)

Relative contributions to RDS(ON) with different Voltage Ratings.
Voltage Rating:
Packaging
RWCML
Metallization
Source
RCH
Channel
JFET Region
REPI
RSUB
Epytaxial Layer
Substrate
50 V
100 V
500 V
Key Parameter
RDS(ON)
V(BR)DSS & RDS(ON) increasing with Junction Temperature.

Normalised V(BR)DSS
Normalised RDS(ON)
1.15
3
1.10
2.5
1.05
2
1.00
1.5
0.95
1
0.90
0.5
0
0
-50
-25
0
25
50
75
100
Junction Temperature [ºC]
125
150
-50
-25
0
25
50
75
100 125
Junction Temperature [ºC]
150
Key Parameter
Qg

Qg : The total gate charge required to charge the device’s input
(Ciss) to the applied voltage.
: The designer is using the Qg (instead of Ciss), to size the gate
drive circuit and to estimate the switching speeds & losses.
CGD
CDS
Ciss = CGS + CGD, CDS shorted
capacitance
Key Parameter
VGS(th)

VGS(th) : is the Gate-to-Source voltage required to achieve surface inversion of
the diffused channel region and as a result, conduction in the channel.
: this value is primarily a function of the Gate oxide thickness and
channel doping level.
Vth - Standard device
- Logic Level device
- Super Logic Level device
- Super2 Logic Level device
= 2 to 4V
= 1 to 2V
= 0.5 to 1.2V
=
(driven by 10V)
(driven by 5V)
(driven by 2.5V)
(driven by 1.8V)
Normalised VGS(th)
1.15
source contact
1.05
source
metal
intermediate dielectric
polysilicon gate
n+
p+
collector
current
1.10
1.00
n+
p+
n+
0.95
n- epy
n+ buffer layer
p+ substrate
Drain Back Metal
0.90
0
-50 -25
0
25
50
75 100 125 150
Junction Temperature [ºC]
Key Parameter
Packages
ST Device Examples
MOSFET
STMicroelectronics
ST Device Example
MOSFETs Nomenclature
ST Device Example
MOSFETs : SO-8/TSOP-6 Nomenclature
MOSFETs : SO-8/TSOP-6 Nomenclature
ST S 4 DN F 30 L
L=Low threshold
V=Super low threshold
Actual voltage [V] upto 80
actual/100 from 100 V up
E=EHD1 (1st gen. STripFET)
F=EHD2 (2nd gen. STripFET)
ES=EHD1+Schottky,...
LOGO
S=SO-8
T=TSOP-6
ID [A]
DN=Dual N-channel
N=Single N-channel
P=Single P-channel
C=Complementary P+N-channel
H=Complementary Half Bridge