High-Speed Optoelectronic Receivers in SiGe

Amit GuptaUniversity of Pittsburgh

Advisors:Dr. Steven P. Levitan

Dr. Donald M. Chiarulli

Goals

• Investigate SiGe HBT as Photodetectors in IBM Blue LogicTM technology– Study the micro fabrication steps of the IBM process– Analyze intrinsic absorption mechanism in SiGe

• Use analog mixed signal design tools to optimize optical receiver circuit– Investigate circuit topologies for transimpedance

amplifiers (TIAs)– Design, simulate, layout and verify several TIAs and

receiver circuits in the IBM process• Test the SiGe optoelectronic receiver chip

Why SiGe for Optical Receivers?• SiGe HBT and CMOS process

compatibility

• Less expensive than GaAs

• Lower power at higher speeds than Silicon

• Possibility of integrating photodetectors at longer wavelengths of 1300nm

• Operation at oscillation frequencies above 65 GHz

SiGe transistor Trade excess

speed forLow power

Sitransistor

Wavelength (µm)

Power1.3µm

Abs

orpt

ion

Coe

ffici

ent α

(cm

-1)

Spee

d

Photon Energy (eV)

Cadence and

Neolinear

Fabricate through MOSIS Test receiver configuration

Build key sub-circuitsfor receiver design

Identify and analyze SiGe photodiode/phototransistor

structures in the IBM SiGe process

Project Flow

Simulation, optimization and verification of receiver circuits based on IBM SiGe BiCMOS process

Investigation and selection of SiGe based high speed

receiver circuits

Photodetector Structure: The Plan

M3 M3

M2 M2 M2 M2

M1 M1 M1 M1 M1 M1 M1

S2 S2S2

S1 S1S1S1

CB CE CC CS CG CD CC

P- Substrate P- SubstrateDT DT DT

ST ST ST ST STN+

N+ N+P+ P+P+

N-WellN-CollectorN-Sub Collector

N+

P+-SiGe

Cross section of the IBM SiGe BiCMOS process

B.S. Meyerson, “Silicon: germanium-based mixed-signal technology for optimization of wired and wireless telecommunications”, IBM J. Res. Develop., Vol. 44, No. 3, pp. 391-407, May 2000 .

Light

Cross section of the IBM NPN transistor with emitter

removed

EMITTER

SiGe Base and Emitter formationEmitter pedestal is created to define emitter opening and to protect the base

Formation of emitter structure over the SiGe base

Emitter opening is created to form emitter structure

Thin Oxide Thin Nitride Thin Polysilicon

Emitter Pedestal

N+

N+P-P+

P-Well

P+ P-P+

Si1-xGex

N-Collector

Subcollector

N+ N+ P-P+

P-Well

P+ P-P+

N-CollectorSubcollector

P+P+P+

Emitter opening SiGe Base

Emitter formation

Harame, D.L., et al., “Si/SiGe epitaxial-base transistors - II. Materials, physics, and circuits”, IEEE Transactions on Electron Devices, Volume: 42 Issue: 3, pp. 455 -468, March 1995.

Photodetectors: Layout• Use the layout of SiGe

NPN transistor as a design start– npn1 p-cell

• Two photodetector designs:– Photo diode:

• Removed emitter– Photo transistor:

• With complete emitter• With emitter partially

removed

BASE

EMITTER

COLLECTOR

Layout of photodetectors was performed by Leo Selavo, CS Department

⊥

Key Components-Optical Receivers

Phototransistor / Photodiode

Transimpedance Amplifier

Output

MultistageDifferential

Amplifier

Decision Circuit

RF

CF

hυ -+

C

EB

hυC

B Vref

Front-End Amplifier-Optical Receiver

• Front-end configurations– Low, high and transimpedance amplifier

• TIAs with same maximum oscillation frequency (fMAX) and designed in other custom SiGe and GaAs processes

• Evaluation of analog CAD tools to optimize TIAs

R R

Rf

Low impedance Transimpedance High impedance

Simulations of TIAs

66.641.84GHz21.498.59GHz21.49700 (Ω)9.9921.57TIA#8

73.532.72GHz47.502.97GHz47.50680 (Ω)3.3346.73TIA#7

69.285.21GHz29.126.01GHz29.12680 (Ω)6.4129.99TIA#6

67.759.49GHz24.419.54GHz24.41630 (Ω)10.9325.52TIA#5

56.678.45GHz6.828.41GHz6.82700 (Ω)10.346.70TIA#4

65.622.19GHz19.119.84GHz19.11700 (Ω)9.9619.60TIA#3

63.269.86GHz14.5610.14GHz14.56430 (Ω)9.9915.04TIA#2

56.329.12GHz6.5510.18GHz6.55700 (Ω)10.116.56TIA#1

4.22GHz

5.78GHz

7.96GHZ

5.45GHz

2.97GHz

8.12GHz

Bandwidth(GHz)

63.69

68.94

63.38

60.03

54.08

55.22

Gain (dB Ω)

Physical Verificationby DIVA

DRC EXT LVS

8.34GHz

7.70GHz

9.04GHZ

7.96GHz

2.94GHz

8.33GHz

Bandwidth(GHz)

15.29

28.01

14.76

10.04

5.06

5.77

Output(mV)

690 (Ω)

580 (Ω)

700 (Ω)

700 (Ω)

100 (Ω)

700 (Ω)

Feedback Resistance

Rf (Ω)

15.29

28.01

14.06

10.04

5.06

5.77

Output(mV)

14.60

31.06

15.03

10.25

5.57

5.70

Output(mV)

12.83TIA#14

11.44TIA#13

10.66TIA#12

10.48TIA#11

5.1TIA#10

10.06TIA#9

Bandwidth(GHz)

Circuit/Topology

66.641.84GHz21.498.59GHz21.49700 (Ω)9.9921.57TIA#8

73.532.72GHz47.502.97GHz47.50680 (Ω)3.3346.73TIA#7

69.285.21GHz29.126.01GHz29.12680 (Ω)6.4129.99TIA#6

67.759.49GHz24.419.54GHz24.41630 (Ω)10.9325.52TIA#5

56.678.45GHz6.828.41GHz6.82700 (Ω)10.346.70TIA#4

65.622.19GHz19.119.84GHz19.11700 (Ω)9.9619.60TIA#3

63.269.86GHz14.5610.14GHz14.56430 (Ω)9.9915.04TIA#2

56.329.12GHz6.5510.18GHz6.55700 (Ω)10.116.56TIA#1

4.22GHz

5.78GHz

7.96GHZ

5.45GHz

2.97GHz

8.12GHz

Bandwidth(GHz)

63.69

68.94

63.38

60.03

54.08

55.22

Gain (dB Ω)

Physical Verificationby DIVA

DRC EXT LVS

8.34GHz

7.70GHz

9.04GHZ

7.96GHz

2.94GHz

8.33GHz

Bandwidth(GHz)

15.29

28.01

14.76

10.04

5.06

5.77

Output(mV)

690 (Ω)

580 (Ω)

700 (Ω)

700 (Ω)

100 (Ω)

700 (Ω)

Feedback Resistance

Rf (Ω)

15.29

28.01

14.06

10.04

5.06

5.77

Output(mV)

14.60

31.06

15.03

10.25

5.57

5.70

Output(mV)

12.83TIA#14

11.44TIA#13

10.66TIA#12

10.48TIA#11

5.1TIA#10

10.06TIA#9

Bandwidth(GHz)

Circuit/Topology

Pre-SimulationPost-Simulation

(RCX)Post-Simulation

(RCX with I/O Pads)

SiGe Optoelectronic Receiver Chip

1 of 16 Transimpedance Amplifiers

2 of 3 SiGe Photodetector Arrays

1 of 3 Receiver Circuits

Input Pad

Output Pad

Ground Pad

Power Supply Pad

Test Setup

Circuit layout

Ground

Probe

Output

Probe

Input

Probe

Supply

Probe

Transimpedance Amplifier # 4

Rc

RF

C1

E1

B1

C2

E2

RE

B2

Q1

Q2

t

Circuit Topology TIA#4

output

Vss

Input

Substrate

Test Results TIA#4 @ 200MHz

0

2

4

6

8

10

12

14

0 20 40 60 80 100

Current(micro-amps)

Vola

tge(

mill

i-vol

ts)

41.6511.595

40.928.980

42.074.737

41.512.521

Gain(dBΩ)

Output Voltage(millivolts)

Input Current(microamps)

41.6511.595

40.928.980

42.074.737

41.512.521

Gain(dBΩ)

Output Voltage(millivolts)

Input Current(microamps)

Current versus voltage characteristics

Current (micro-amps)

Volta

ge (m

illi-v

olts

)

(Simulation 56.67dBΩ@8.45GHz)

Transimpedance Amplifier # 6

Q1

Q2Q3

Q4

Rf

Q5

Re2Re1

t

Circuit Topology TIA#6

output

Vss

Input

Substrate

RERE RE RE

Test Results TIA # 6 @ 50MHz

0.00E+002.00E-014.00E-016.00E-018.00E-011.00E+001.20E+001.40E+001.60E+001.80E+002.00E+00

-2.00E-01 -1.50E-01 -1.00E-01 -5.00E-02 0.00E+00 5.00E-021.00E-01

1.20E-01

1.40E-01

1.60E-01

1.80E-01

2.00E-01

2.20E-01

2.40E-01

-2.00E-01 -1.50E-01 -1.00E-01 -5.00E-02 0.00E+00 5.00E-02

Input waveform at 50MHz Output waveform at 50MHz

(Simulation 69.28dBΩ@5.21GHz)

Volta

ge (V

)

Time (µsec)

Test Results TIA#6 @ 200MHz

Input waveform at 200MHz Output waveform at 200MHz

Volta

ge (V

)

Time (µsec)

4.00E-01

6.00E-01

8.00E-01

1.00E+00

1.20E+00

1.40E+00

1.60E+00

-2.00E-01 -1.50E-01 -1.00E-01 -5.00E-02 0.00E+00 5.00E-021.20E-011.30E-011.40E-011.50E-011.60E-011.70E-011.80E-011.90E-012.00E-012.10E-01

-2.00E-01 -1.50E-01 -1.00E-01 -5.00E-02 0.00E+00 5.00E-02

Receiver Circuit # 1

Q1 Q2 Q3 Q4 Q5 Q6

Q8Q7

N1 N2 N3

P1

N4

TransimpedanceAmplifier # 6

Three Cascaded Differential Amplifying Stages

Buffer

StageDecision

Circuit

Output Results-Receiver #1Output -TIA

Output1- Differential Amplifier1

Output2- Differential Amplifier1

Output- Differential Amplifier2

Output- Differential Amplifier3

Output- Buffer

Output- Decision Circuit

Output -TIA

Output1- Differential Amplifier1

Output2- Differential Amplifier1

Output- Differential Amplifier2

Output- Differential Amplifier3

Output- Buffer

Output- Decision Circuit

Input Current-10µA

Conclusion• SiGe Photodetector intrinsic absorption in IBM

process is predicted up to 1150nm • NeoCircuit successfully automated the

transistor sizing and bias voltages• NeoCell efficiently performed auto place and

route• SiGe 5HP CMOS (0.5micron) lacks 10 GHz

performance• Preliminary testing of transimpedance amplifiers

show promising results