A New Generation of Power Semiconductor Devices

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A New Generation of Power Semiconductor Devices
A New Generation of Power Semiconductor
Devices
JoséMillán
Centro Nacionalde Microelectrónica, CNM
CNM-CSIC, Campus UniversitadAutónomade Barcelona,
08193 Bellaterra, Barcelona, Spain
A New Generation of Power Semiconductor Devices
•Introduction
•Si Power Devices
•Si IGBTs
•Si Super-junctions
•SiCPower Devices
•SiCPower Rectifiers
•SiCPower Switches
•GaNPower Devices
•WBG Future Trends
Outline
A New Generation of Power Semiconductor Devices

efficient processing of electrical energy through means of
electronic switching devices

Power Electronics is:
40% of Energy
consumed as
electricity
Introduction
A New Generation of Power Semiconductor Devices
Traction/Automotive
Communications
Energy Distribution
Introduction
A New Generation of Power Semiconductor Devices
Classification of High Voltage
Devices
Power Devices
A New Generation of Power Semiconductor Devices
Si Power Devices
Si Power Devices
A New Generation of Power Semiconductor Devices
GTO, Power MOSFET and Cool MOS
Voltage Range
Power MOSFET
Cool MOS
GTO Thyristor
Power
supplies
Electric
cars
Motor
control
Traction
& HVDC
Si Power Devices
A New Generation of Power Semiconductor Devices
IGBT Structure & Output Characteristics
Structure of ‘DMOS’IGBTStatic Characteristics
Currentx10 comparedwithpowerMOSFET
Si IGBTs
A New Generation of Power Semiconductor Devices
IGBT OFF-state
The p -base/n-base
junction blocks the voltage
while the device is in the
off-state
Si IGBTs
A New Generation of Power Semiconductor Devices
IGBT ON-state
-
When the device is in the
on-state the electron
current at the cathode flows
through the channel like in a
MOSFET and acts as the
base current for the pnp
transistor formed between
the p+ anode-(emitter), n-
base & n+ buffer (base)
and p-base (collector).
Due to high level of
injection in the on-state the
entire n-base is modulated
by mobile carriers in
equilibrium with an
effective charge of few
orders of magnitude higher
than the original doping
Si IGBTs
A New Generation of Power Semiconductor Devices
p
+
n-drift
region
Source/Cathode
Gate
Source/Cathode
Anode
n
+
n
+
p well
p well
p+
p+
The IGBT has within its structure three MOS-bipolar devices:
(i) The cascade MOSFET -PIN diode
(ii) MOS base current controlled -wide base PNP transistor
(iii) Parasitic MOS turn-on thyristor -must be always
suppressed
The IGBT Equivalent Circuit
Si IGBTs
A New Generation of Power Semiconductor Devices
IGBT turn-off Characteristics
(2)
(3)
(4)
(1)
Examples of measured IGBT turn-off characteristics in inductive conditions.
The characteristics are plotted for different rail voltages. There are three
distinctive regions (1) voltage rise (2) electron current fall, (3) removal of
main charge stored in the drift region (4) current tail through recombination
Si IGBTs
A New Generation of Power Semiconductor Devices
Three concepts that led to major
advancements in IGBTs from one
generation to another
•Trench and thin wafer technologies –led to
~30 % cut in the on-state voltage drop
•PIN diode effect –Enhanced injection of
electrons at the top side (channel side) of the
drift region –led to a further 20% decrease in
the on-state voltage drop
•Field stop (Soft Punch Through) technology led
to ~20% cut in the turn-off losses and 10-20%
decrease in the on-state voltage drop
Si IGBTs
A New Generation of Power Semiconductor Devices
PT & NPT IGBT Structures
Punch-Through (PT IGBT)
Non Punch-Through (NPT IGBT)
Ecr
Ecr
Safety
distance
Si IGBTs
A New Generation of Power Semiconductor Devices
Trench IGBT Cross Sections
Schematic
Schematic
SEM
SEM
4μm
5μm
Si IGBTs
A New Generation of Power Semiconductor Devices
Breakdown vson-state in DMOS IGBT & Trench
IGBT
Si IGBTs
A New Generation of Power Semiconductor Devices
The ability to ‘engineer’the PIN diode section in
the TIGBT can be used to optimiseits performance
The heavily charged accumulation layer
serves as an electron injector forming a
PIN diode with n-drift region and p-anode
There are two paths for the current flow:
(i) the double sided injection path of the
PIN diode with increased plasma at both
injection ends (anode and cathode end),
and
(ii) the pnppath with increased plasma
only at the IGBT anode end.
Increasing the PIN diode contribution
over that of the pnptransistor is the key
to enhance the device performance
This is equivalent to suppressing the
collection of holes by the p well to the
cathode short
n buffer
n-drift region
Cathode
Anode
n+n+
p -well
p -well
Gate
Channel
Cathode
P anode
p+p+
Electron
injector
Si IGBTs
A New Generation of Power Semiconductor Devices
On-state Characteristics of a TIGBT
Si IGBTs
A New Generation of Power Semiconductor Devices
The Field Stop (or Soft Punch-Through),
PT and NPT structures
n-buffer –field stop
P transparent anode
p+
(substrate)
n-drift
region
Gate
Source/Cath
n
+
p well
250
μ
m
120
μ
m
N-buffer
15
μ
m
P transparent
anode
n
+
p well
200
μ
m
1
μ
m
n-drift
region
n
+
p well
120
μ
m
1-2
μ
m
1
μ
m
PT -IGBT
NPT -IGBTSPT -IGBT
Source/CathGateGate
Source/Cath
Si IGBTs
A New Generation of Power Semiconductor Devices
The Field Stop (or Soft Punch-Through),
PT and NPT comparison
Structure
PT -IGBT
NPT -IGBT
SPT -IGBT
Drift layer thickness
thin
thick
thin
Wafer type (for 600 V
and 1.2 kV)
Epitaxial
Float zone (FZ)
Float Zone (FZ)
Buffer Layer
Thick and highly doped
N/A
Thin and lowly doped
P+ anode injector
Thick and highly doped
(whole substrate)
Thin and relatively
lowly doped
Thin and relatively
lowly doped
Bipolar gain control
Lifetime killing
Injection efficiency
Injection efficiency
On-state losses
low
medium
low
Switching losses
high
medium
low
Turn-off tail
short
long
short
Voltage overshoot (in
some applications)
high
low
low
Temperature coefficient
negative (mostly)
positive
positive
SCSOA (short circuit
conditions)
medium
large
large
RBSOA (reverse bias
conditions)
narrow
large
large
Structure
PT -IGBT
NPT -IGBT
SPT -IGBT
Drift layer thickness
thin
thick
thin
Wafer type (for 600 V
and 1.2 kV)
Epitaxial
Float zone (FZ)
Float Zone (FZ)
Buffer Layer
Thick and highly doped
N/A
Thin and lowly doped
P+ anode injector
Thick and highly doped
(whole substrate)
Thin and relatively
lowly doped
Thin and relatively
lowly doped
Bipolar gain control
Lifetime killing
Injection efficiency
Injection efficiency
On-state losses
low
medium
low
Switching losses
high
medium
low
Turn-off tail
short
long
short
Voltage overshoot (in
some applications)
high
low
low
Temperature coefficient
negative (mostly)
positive
positive
SCSOA (short circuit
conditions)
medium
large
large
RBSOA (reverse bias
conditions)
narrow
large
large
Si IGBTs
A New Generation of Power Semiconductor Devices
1.2 kV IGBTs. SPT has a better carrier profile than the
PT and NPT structures with the Trench SPT showingthe
most favorable result.
Si IGBTs
A New Generation of Power Semiconductor Devices
The trade-off between on-state voltage and turn-off energy
losses for 1.2 kV DMOS PT IGBT, the Trench IGBT and the
Trench SPT IGBT
Si IGBTs
A New Generation of Power Semiconductor Devices
n+n+
H. Takahashi, 1.2 kV Reverse Conducting
IGBT (ISPSD 2004), Mitsubishi
M. Rahimo, 3.3 kV RC IGBT using SPT+
technology (ISPSD 2008)
The Reverse Conducting IGBT
Si IGBTs
A New Generation of Power Semiconductor Devices
The Reverse Blocking IGBT
•600V RB-IGBT designed and fabricated at CNM
•Additional protection of IGBT periphery: trench isolation (patent pending)
•Applications: Current inverters, resonant converters, Matrix converters,
BDS
N
Al
SiO
2
Poly Si
P
+
Junction supporting
forward bias
Body-P
Epitaxy -N
Substrate-P
Substrate-P
+
+
-
Junction supporting
reverse bias
-800-600-400-2000200400600800
-1,25
-1,00
-0,75
-0,50
-0,25
0,00
0,25
0,50
0,75
1,00
1,25
I
C
(mA)
VCE (V)
RB-IGBT
(G-E short)
3328-RBI Wafer 11 Bidirectional Blocking Capability
Si IGBTs
A New Generation of Power Semiconductor Devices
Super-JunctionMOSFETS
COOLMOS
Rectangular e-fielddistribution
allowsincreasingNepidoping.
RonxAbelowSi limit
Si Super-junctions
A New Generation of Power Semiconductor Devices
WBG Power Devices
WBG Semiconductors
A New Generation of Power Semiconductor Devices
•Si devices are limited to operation at
junction temperatures lower than 200 ºC
•Si power devices not suitable at very high
frequencies
•SiCand GaNoffer the potential to overcome
both the temperature, frequency and power
management limitations of Si.
Why WBG Semiconductors?
WBG Semiconductors
A New Generation of Power Semiconductor Devices
Physical properties of WBG for Power Devices
Material
Eg
(eV)
@300K
μn
(cm²/Vs)
μp
(cm²/Vs)
Vsat
(cm/s)
Ec
(V/cm )
λ
(W/cm.ºK)
εr
Si
1.12
1450
450
107
3×105
1.3
11.7
4H -SiC
3.2
950
115
2 ×107
3 ×106
5
10
GaN
3.39
1000
350
2 ×107
5 ×106
1.3
8.9
Diamond
5.6
2200
1800
3 ×107
5 ×107
20
5.7
WBG Semiconductors
A New Generation of Power Semiconductor Devices
•GaN& SiCprocess technologies are more mature
•At present, SiCis considered to have the best trade-off
between properties and commercial maturity
•GaNcan offer better HF and HV performances, but the
lack of good quality large area substrates is a
disadvantage for vertical devices
•GaNpresents a lower thermal conductivity than SiC
•GaNallows forming 2DEG heterojunctions(InAlGaN
alloys) grown on SiCor Si substrates
•Currently, it is a sort of competition SiCvsGaN, in a
battle of performance versus cost
•There is not a clear winner at the moment. They will
find their respective application niches with a
tremendous potential market
WBG Technology
A New Generation of Power Semiconductor Devices
SiCPower Devices
SiCPower Devices
A New Generation of Power Semiconductor Devices
•SiCPower Rectifiers
•Schottkybarrier diodes (SBD): extremely high switching speed but
lower blocking voltage and high leakage current.
•PiNdiodes: high-voltage operation and low leakage current, reverse
recovery charging during switching.
•Junction Barrier Schottky(JBS) diodes: Schottky-like on-state and
switching characteristics, and PiN-like off-state characteristics.
SiCPower Diodes
A New Generation of Power Semiconductor Devices
State-of-the-Art
SiCrectifiers•
Schottkyand now JBS diodes are commercially available up to
1.2 kV: CREE, Infineon basically.

PiNdiodes will be only relevant for BV over 3 kV.
-Need to overcome its reliability problem (forward
voltage drift) before commercialisation
SiCPower Diodes
A New Generation of Power Semiconductor Devices
SiCPower Switches
A New Generation of Power Semiconductor Devices
•Very low Ron
•Rugged Gate-structure
•Excellent short-circuit
capability
•High temperature possible
Main problem: Normally on (?)
x
SiCPower Switches (unipolar)
A New Generation of Power Semiconductor Devices
•Compared to a COOLMOS –
based converter, the SiC-
based one offers the
highest efficiency (90%)
•All SiCsparse matix
converters
•CoolMOS+ SiCÆefficiency
higher than 96%
Hybrid Si/SiCcascodeelectric switch
•All SiCsparse matrix converter: 100 KHz –1.5 kW –efficiency
94% 1300V 4 A SiCEDCascodes+ 1200 V 5 A CREE Schottky
diodes
•3 phase PWM rectifier 10kW –500KHz –480V CoolMOS+ SiC
Schottkydiodes : efficiency higher than 96%
SiCPower Switches (unipolar)
A New Generation of Power Semiconductor Devices
•Simple planar structrure
•Voltage gate control
•Extensively used in Si
technology
•Normally-off
•Low channel mobility in SiC
•High temperature operation ?
•Gate reliability ?
MOSFET main problems
x
MOSFET Advantages
9
Trench/DiMOSFET
Lateral DMOFET
SiCPower Switches (unipolar)
A New Generation of Power Semiconductor Devices

CREE: 2.3KV-5A Ron=0.48 Ω(25ºC) 13.5mΩ.cm
2,
Ir=200uA. Cin=380pF, Cout=100pF, reverse transfer
C=19pF (Vgs=0,Vds=25V, 1MHz)

Infineon: 1200V-10A, Ron=0.27 Ω(25ºC) 12mΩ.cm
2

Denso:
1200V-10A, 5 mΩ.cm2
(25ºC), 8.5mΩ.cm2
(150ºC)
SiCPower Switches (unipolar)
A New Generation of Power Semiconductor Devices
10 kV MOSFET
(Cree)
[M. Das et al. at ISPSD’2008, pp. 253-259]
SiCPower Switches (unipolar)
A New Generation of Power Semiconductor Devices

3500 V -6500 V range

Unlike Si BJT, SiCBJT does not
suffer from a secondary breakdown

ßis reduced (50%) under bias
stress (stacking faults base-emitter
region)
•4 kV, 10 A BJT
•βmax= 34
•chip area = 4.24 mm ×4.24
mm
•IR =50 µA @ 4.7 kV
•turn-on time = 168 ns @ RT
•turn-off time = 106 ns @ RT
State-of-the-art
[S. Krishnaswamiet al.,
ISPSD’2006, pp. 289-292]
SiCPower Switches (bipolar)
A New Generation of Power Semiconductor Devices
•Problems of MOSFETS (Channel mobility,
reliability)
•Problems of Bipolar (current gain degradation,
stacking faults)
•Problems of highly doped P substrate growth
SiCIGBT?
•May 2008 (ISPSD 2008): CREE 10kV n-channel IGBT
•3V knee, 14.3 mΩcm
2
•At 200ºC the n-IGBT operates at ×2 the current
density of the n-MOSFET
SiCPower Switches (bipolar)
A New Generation of Power Semiconductor Devices
GaNPower Devices
GaNPower Devices
A New Generation of Power Semiconductor Devices
GaNPower Rectifiers •Until recently, because of the lack of electrically
conducting GaNsubstrates, GaNSchottkydiodes were
either lateral or quasi-vertical
•Breakdown voltages of lateral GaNrectifiers on
Sapphire substrates as high as 9.7 kV have been
reported
Zhang et al.
IEEE T-ED,48, 407, 2001
SBD
PiN
GaNPower Diodes
A New Generation of Power Semiconductor Devices
GaNPower HEMTs •GaNHEMTshave attracted most attention with impressive
trade-off between Ron vsBV
•Power densities 1.1 W/mm in 1996 initially to microwave
power HEMTswith high output power capability as high as
40 W/mm recently
•A major obstacle trapping effects though drain-current
collapse
•Several solutions :
•(1) surface-charge-controlled n-GaN-capstructure
•(2) the recessed gate and field-modulating plate
structure
•(3) passivationof surface states via silicon nitride or
other dielectric.
GaNPower HEMTs
A New Generation of Power Semiconductor Devices
•High voltage AlGaN/GaNHEMTsover 1 kV were reported in
2006
•It has been also demonstrated a GaNpower switch for kW
power conversion.
•The switch shows a speed grater than 2 MHz with rise-and
fall-time of less than 25 ns, and turn-on/turn-off switching
losses of 11 µJ with a resistive load.
•Switching at 100 V/11 A and 40 V/23 A was achieved with
resistive and inductive loads, respectively.
S. YOSHIDA et al.ISPSD 2006
GaNPower HEMTs
A New Generation of Power Semiconductor Devices
Y. Uemotoet al.IEDM 2007
8.3 kV HEMT
(Panasonic)
Via-holes through sapphire at the
drain electrodes enable very
efficient layout of the lateral HFET
array as well as better heat
dissipation
GaNPower HEMTs
A New Generation of Power Semiconductor Devices
The state-of-the-art AlGaN/GaNHEMT[T. Nomura et al., ISPSD 2006, pp. 313-316]
•Process technology based on a tri-metal Ti/AlSi/Mo layer

very low contact resistance and an excellent surface
morphology.
•Mo (barrier metal) to improve the surface morphology
•AlSiresults more efficient for a low contact resistance
than Al.
•Low stress, high-refractive index SiNx
layer →
Gate leakage current as low as 10
-7
A/mm.
•Ron
= 6.3 mΩ.cm2, VBR
= 750 V.
•Turn-on time: 7.2 ns (1/10 of Si MOSFET).
•Switching operation no significant degraded at 225ºC.
GaNPower HEMTs
GaNPower HEMTs
A New Generation of Power Semiconductor Devices
The state-of-the-art normally-off AlGaN/GaNHEMT[N. Kanekoet al. , ISPSD 2009, pp. 25-28]
•RecessgateelectrodeandNiOx
as gateelectrode
(NiOxoperatesas a p-type)
•Wgate= 157 mm, Vth
= +0.8 V
•Ron
×A = 6.3 mΩ.cm2
•Ron
= 72 mΩ
•VBR
> 800 V
•IDmax
> 20 A
Thegateleakagecurrentfourordersofmagnitudesmallerthan
theconventionalnormally-onHFETs.
GaNPower HEMTs
GaNPower normally-off AlGaN/GaNHEMTs
A New Generation of Power Semiconductor Devices
Lateral GaNMOSFETs

LateralMOSFETshave been fabricated on p-GaNepilayer
(MOCVD) on sapphire substrates
[W. Huang et al., ISPSD 2008, pp. 291].
-
High quality SiO2/GaN interface
-
2.5 kV breakdown voltage
-
High channel mobility (170 cm
2/V.s)
•Lateral GaNMOSFETscan compete with SiCMOSFETsand GaN
HEMTs?
•Reduction of source/drain resistance is crucial to further
reduce the device on-resistance.
GaNPower MOSFETs
A New Generation of Power Semiconductor Devices
WBG Future Trends
SiCSwitches •Successful demonstration of the cascodepair (a high-
voltage, normally-on SiCJFET + a low-voltage Si
MOSFET).
•An industrial normally-off SiCswitch is expected. It
could be the SiCMOSFET (<5kV) or the SiCIGBT
(>5kV).
•BJTs/Darlingtonsare promising, they also suffer from
reliability problems.
•A normally-off SiCpower transistor in the BV range of
600V-1200V available within next two years.
WBG Future Trends
A New Generation of Power Semiconductor Devices
GaNPower Devices •GaNis already commercialised in optoelectronics.
•Its applications in power switching still require
further work in materials, processing and device
design.
•GaNHEMT (5-10 A, 600-1200 V normally-off)
•It will be interesting to see if GaNpower devices,
especially low cost Schottkydiode, can overtake or
displace SiCdiodes.
GaNPower HEMTs
WBG Future Trends
A New Generation of Power Semiconductor Devices
Thanks for your attention