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High Current Density and High Power Density Operation of Ultra High Speed InP DHBTs . Mattias Dahlström 1 , Zach Griffith, Young-Min Kim 2 , Mark J.W. Rodwell Department of ECE University of California, Santa Barbara, USA. (1) Now with IBM Microelectronics, Essex Junction, VT - PowerPoint PPT Presentation
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High Current Density and High Power Density Operation of Ultra High Speed InP DHBTs
Mattias Dahlström1, Zach Griffith,Young-Min Kim2, Mark J.W. Rodwell
Department of ECEUniversity of California, Santa Barbara, USA
[email protected] 805-893-8044, 805-893-3262 fax
(1) Now with IBM Microelectronics, Essex Junction, VT(2) Now with Sandia National Labs, NM
Overview
• Fast devices and circuits need high current!– Current limited by
• Kirk current threshold• Device heating
– Thermal resistance Device heating • Design of low thermal resistance HBT• High Current Devices with state of the art
RF performance
The need for high current density
0
5
10
15
20
25
30
35
1010 1011 1012
Gai
ns (d
B)
Frequency (Hz)
ft = 370 GHz
fmax
= 459 GHzU
H21
MAG/MSG
Ajbe
= 0.6 x 7 um2
Ic = 35 mA
Jc = 8.3 mA/um2, V
cb= 0.35 V
bccexbcicjeiece
Bcb
bccexbcjec
Bcb
CRRCACAJqATnk
f
CRRCCqITnk
f
,,21
21
Scaling laws:Single HBT: f
-80
-70
-60
-50
-40
-30
-20
-10
0
50 55 60 65 70 75
Out
put P
ower
(dB
m)
frequency (GHz)
-80
-60
-40
-20
0
59.34 59.36 59.38 59.40 59.42
dBm
GHz
divide by 2
Je=6.9 mA/m2
Output spectrum @ 59.35 GHz, fclk=118.70 GHz
. ...and
, , , , logiclogic
logiclogic
f
c
bb
c
ex
c
je
c
cb
IVR
IVRV
IC
VIC
Minimize capacitance charging times! Increase current density
Digital circuitKey performance parameters:
Je=8 mA/m2
0
20
40
60
80
100InPInAsInGaAsInAlAsInGaPGaAsSiSiNSiOpolyimid
(W
/Km
)
Material
InP
InAs
InGaAsInAlAs
InGaP
GaAs
Si (168)
SiN SiO polyimid
at 300 K
Thermal conductivity of common materials
Ternaries lattice matched to InP
HBT: Where is the heat generated?
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
50 100 150 200 250 300 350
E (e
V)
Position (A)
Ec
EvEmitter
Collector
Base
InGaAs
InGaAs
InGaAs
InP
InP
InGaAlAs
Vbe = 0.95 V, Vce = 1.3 V
Power generation: JE x VCE=6 x 1.5 V=9 mW/m2
In the intrinsic collector
HBT: heat transport
Main heat transport is through the subcollector to the substrateUp to 30 % heat transport up through the emitter contact
Thermal resistance of materials in collector and subcollector critical
How to design a low thermal resistance HBT
A five step process
Identify high thermal resistance materials change them low thermal resistance materials Very simple!
SHBT: InGaAs collector
Design of low thermal resistance HBT:Initial design: InGaAs collector
SHBT: InGaAs collector, InP emitter
Design of low thermal resistance HBT:Emitter: InAlAsInP
DHBT: InGaAs/InP collector
Design of low thermal resistance HBT:InGaAs collector InP collector with InGaAlAs grade
DHBT: InGaAs/InP collector, InGaAs/InP subcollector
Design of low thermal resistance HBT:InGaAs subcollector InGaAs/InP composite subcollector
DHBT: InGaAs/InP collector, thin InGaAs/InP subcollector
Design of low thermal resistance HBT:Thick InGaAs in subcollector thin InGaAs in subcollector
Metamorphic-DHBT: InGaAs/InP collector, InGaAs/InP subcollector
Design of low thermal resistance Metamorphic HBT:InAlAs,InAlP, InGaAs buffersInP buffer
Young-Min Kim
CfixedIc
CE
BE
CfixedIc
CE
BEJA
CECJACECE
BEfixedIcBE
IVV
IdVdV
VIVdVdP
dPdT
dTdVV
11
Experimental Measurement of Temperature Rise
Temperature rise can be calculated by measuring IC, VCE and VBE
BEV
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98
I c (A
)
Vbe
(V)
Meta run 11 (BCB)E05B05
V3.1ceV
cI
V5.1ceV
No thermal instability as long as slope<∞each VBE gives a unique IC
Thermoelectric feedback coefficient (data from W. Liu)
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0.002
0.0022
0.001 0.01 0.1 1 10
(V
/K)
Je (mA/m2)
Thermoelectric feedback coefficient from Liu et al.
Thermoelectric feedback coefficient for AlGaAs/GaAs HBTs 4 % smallerNot a large influence from material or structure variations
W. Liu: “Thermal Coupling in 2-Finger Heterojunction Bipolar Transistors”, IEEE Transactions on Electron Devices, Vol 42 No6, June 1995W. Liu: H-F. Chau, E. Beam, "Thermal properties and Thermal Instabilities of InP-Based Heterojunction Bipolar Transistors”, IEEE Transactions on Electron Devices, Vol 43 No3, March 1996
Compared to previous UCSB mesa HBT results:
• Thinner InP collector—decrease c
• Collector doping increased—increase JKirk
• Thinner InGaAs in subcollector—remove heat
• Thicker InP subcollector—decrease Rc,sheet
High f DHBT Layer Structure and Band DiagramVbe = 0.75 V, Vce = 1.3 V
Emitter
CollectorBase
InGaAs 3E19 Si 400 Å
InP 3E19 Si 800 Å
InP 8E17 Si 100 Å
InP 3E17 Si 300 ÅInGaAs 8E19 5E19 C 300 Å
Setback 3E16 Si 200 Å
InP 3E18 Si 30 Å
InP 3E16 Si 1030 Å
SI-InP substrate
Grade 3E16 Si 240 Å
InP 1.5E19 Si 500 Å
InGaAs 2E19 Si 125 Å
InP 3E19 Si 3000 Å
Thermal resistance results: lattice matched
0
0.5
1
1.5
2
2.5
3
3.5
4
05
1015
2025
30
10 15 20 25 30
25 nm InGaAs, polymimide Rth12.5 nm InGaAs, polymimide Rth12.5 nm InGaAs, BCB Rthnew
25 nm InGaAs, polymimide 12.5 nm InGaAs, polymimide 12.5 nm InGaAs, BCB
Ther
mal
resi
stan
ce (K
/mW
)
Temperature rise (K
)
Base-Collector Area (m2)
Measured thermal resistances for lattice matched HBTs. Ic= 5 mA, Vce=1.5 V, P=7.5 mW
25 nm InGaAs
12.5 nm InGaAs
Device Buffer (m)
Tc (nm) Tsc InGaAs (nm)
Tsc InP (nm)
JA K/mW
DHBT-M1 - 200 25 125 2.5
DHBT-19b - 150 12.5 300 1.8
DHBT-23 - 150 12.5 300 1.4
50 nm InGaAs 25 nm InGaAs: large improvement
Thermal resistance results: metamorphic
Measured thermal resistances for metamorphic HBTs. Ic= 5 mA, Vce=1.5 V, P=7.5 mW
25 nm InGaAsInP buffer
0
2
4
6
8
10
12
14
020
4060
8010
0
5 10 15 20 25 30 35
InAlP buffer, 25 nm InGaAs RthInP buffer, 25 nm InGaAs RthInP buffer, 12.5 nm InGaAs Rth
InAlP buffer, 25 nm InGaAsInP buffer, 25 nm InGaAsInP buffer, 12.5 nm InGaAs
Ther
mal
resi
stan
ce (K
/mW
)
Temperature rise (K
)
Base-Collector Area (m2)
50 nm InGaAsInAlP buffer
InAlP InP buffer: large improvement50 nm InGaAs 25 nm InGaAs: small improvement
Device Buffer (m) Tc (nm) Tsc InGaAs (nm)
Tsc InP (nm)
JA K/mW
M-HBT-1 InAlP 1.5 200 50 125 7.6
M-HBT-2 InP 1.5 200 50 125 3.3
M-HBT-11 InP 1.5 200 25 300 3.1
Device and circuit results
0
5
10
15
20
25
30
35
1010 1011 1012
Gai
ns (d
B)
Frequency (Hz)
ft = 370 GHz
fmax
= 459 GHzU
H21
MAG/MSG
Ajbe
= 0.6 x 7 um2
Ic = 35 mA
Jc = 8.3 mA/um2, V
cb= 0.35 V
Zach Griffith
Continuous operation at high current densities greater than peak rf performance (Je = 8 mA/m2)
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2
J e (mA/
m2 )
Vce (V)
Ajbe
= 0.5 x 7 m2
Ib step
= 0.4 mA
Vcb
= 0 V
28 transistor static frequency divider @ fclk=118.7 GHz shownTo be reported, 150 GHz static divider using same Type 1 DHBT structure—chirped superlattice
Transistor operation at 13 mA/m2 150 nm InGaAs/InP collector
370 GHz ft at Jc>8 mA/m2
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0 50 100 150
Out
put S
igna
l (V
)
time (ps)
-80
-70
-60
-50
-40
-30
-20
-10
0
50 55 60 65 70 75
Out
put P
ower
(dB
m)
frequency (GHz)
-80
-60
-40
-20
0
59.34 59.36 59.38 59.40 59.42
dBm
GHz
divide by 2
Our Mesa DHBTs have Safe Operating AreaExtending beyond High-Speed Logic Bias Conditions
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8
J e (mA/
m2 )
Vce (V)
Ajbe
=0.6 x 7 m2 Ib step
= 0.4 mA0.5 um X 0.7 um emitter junction0.5 um base contact width
~6.8 V low-currentBVCEO
0
2
4
6
8
10
12
0 1 2 3 4 5 6
device failure
18 mW/um2
design limit 10 mW/um 2
J max
(mA
/um
2 )
Vce
(V)
8 m emitter metal length, ~0.6 m junction width
biased without failure (DC-IV)
No RF driftafter 3-hr burn-in ECL
bias points
Low-current breakdown is > 6 Volts
this has little bearing on circuit design
Safe operating area is > 10 mW/um2
these HBTs can be biased ....at ECL voltages
...while carrying the high current densities needed for high speed
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2
J e (mA/
m2 )
Vce (V)
Ajbe
= 0.5 x 7 m2 Ib step
= 0.4 mAV
cb = 0 V
peak (f, f
max) bias
Conclusions
• DHBT design with InP subcollector very low thermal resistance
•Metamorphic DHBT with InP buffer low thermal resistance
•DHBT operation at Jc>13 mA/m2
•Optimal device and circuit performance at Jc up to 8 mA/m2
•HBT I-V operating area allows static frequency dividers operating at speeds over 150 GHz
Backup slides
HBT
Why is thermal management important?
• As J increases so does the power density. This will lead to an increase in the temperature.
TC JKirk LeÅ mAμm-2 μm
3000 1.0 81
2000 2.3 34
1500 4.1 19
1000 9.8 8.6
For VCE=1V PD=10.6mWμm-3
V=2V
80mA
For VCE=1V PD=98mWμm-3!!
Thermal Modeling of HBT (1)
• 3D Finite Element using Ansys 5.7• K (Thermal conductivity) depends temperature
• K depends on doping • For GaAs heavily doped GaAs 65% less than undoped GaAs• Unknown for InP or InGaAs use GaAs dependency
n
T Tkk
300300
J.C.Brice in “Properties of Indium phosphide” eds S Adachi and J.Brice pubs INSPEC London p20-21S Adachi in “Properties of Latticed –Matched and strained Indium Gallium Arsenide” ed P Bhattacharya pubs INSPEC London p34-39“CRC Materials science and engineering handbook”, 2nd edition ,eds J.F Shackelford,A.Alexander, and J.S Park, pubs CRC press, Boca Raton, p270
Material K300 n K300(exp) Refs
InP 0.68 1.42 0.68-0.877 1
InGaAs 0.048 1.375 0.048-0.061 2
Au 3.17 - 3
Large uncertainty
in values
Validation of Model
0
5
10
15
20
25
30
35
40
-0.2 0 0.2 0.4 0.6 0.8 1 1.2
centerEdge
Tem
pera
ture
Ris
e (K
)
Distance from substrate (m)
SC ES C B E E Metal
Caused by Low K
of InGaAsMax T in Collector
Ave Tj (Base-Emitter) =26.20°CMeasured Tj=26°CGood agreement.
Advice Limit InGaAs Increase size of emitter arm
Ian Harrison
Analysis of 40,80,160 Gbit/s devices• To obtain speed inprovements require to scale other device
parameters.Speed (Gbit/s) 40 80 160
Collector Thickness (Å) 3000 2000 1000
Base Sheet resistance () 750 700 700
Base contact resistance (-m2) 150 20 10
Base Thickness (Å) 400 300 250
Base Mesa width ( m) 3 1.6 0.4
Current Density (mA/m2) 1 2.3 9.8
Emitter. Junction Width ( m) 1 0.8 0.2
Emitter Parasitic resistivity (-m2) 50 20 5
Emitter Length ( m) 6 3.3 3.2
Predicted MS-DFF (GHz) 62 125 237
Ft (GHz) 170 260 500
Fmax (GHz) 170 440 1000
Tj (K) 7.5 14 28
TMax (K) 10 20 49
TMax (No Etch Stop layer) (K) 7.5 13 21
Conservative 1.5x bit rate
Reduction of parasitic CBC
Device parameters after Rodwell et al
When not switching values will double
V=0.3V
6mA
Ian Harrison
Mesa DHBT with 0.6 m emitter width, 0.5 m base contact width Z. Griffith, M Dahlström
How we measure thermal resistance
Layout improvement: Emitter heat sinking
Emitter interconnect metal 2 μm to 7 μm~30 % of heat out through emitter Negligible increase in Cbe
Improved emitter heatsinking