substrate coupling for 500ghz hbts - tu dresden...• 𝑓𝑚𝑎𝑥𝑓 for high frequencies as...

AK Bipolar, Campeon Munich

November 14, 2012

IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany www.ihp-microelectronics.com © 2012

Substrate Coupling for 500GHz HBTs

Dr. Gerhard Fischer

Substrate Network @ AK Bipolar 2012 2 © 2012 - All rights reserved

Problem: Power Gain or fmax Above 100 GHz

Strong

function of

substrate

resistance!

Don’t care

for

substrate

resistance!

GU(f) as function of Rsub = 1Ω …1kΩ


Starting Point

• It is well-known that

𝑓𝑚𝑎𝑥 𝑓 = Mag(𝐺𝑈)0.5 ∙ 𝑓

is not constant in general.

• Assuming other parameters like base and collector resistances, collector-substrate

and collector-base capacitances, NQS parameters to be fixed.

• 𝑓𝑚𝑎𝑥 𝑓 for high frequencies as function of the “substrate network” has to be

worked out

for Gummel-Poon substrate resistor RSub in series to CCS,

for HICUM CSub parallel to RSub added (because of substrate permittivity).


Fmax (Frequency) as Function of Rsub

Minimum fmax for

RSub ≈ 100 Ω

0 200 400 600 800 1000

350

400

450

500

Extr

ap

ola

ted

fm

ax @

30

0 G

Hz

Substrate Resistance [ Ohm ]


Simulation of CCS(f)

Substrate Ring Variations


Determination of Substrate RC Network

• DUT: HBT (Emitter area: 4x0.13x10.16 µm²) with guard ring variations:

Variable distance active collector – guard ring

1 µm

3 µm

20 µm


CCS(V) as Function of Frequency I

• From S parameters: 𝐶𝐶𝑆 =Imag 𝑌22+𝑌12

2𝜋𝑓

Distance DUT – Guard Ring:

1 µm

3 µm

20 µm

Simulation with constant

RSub = 10 Ω



2𝜋𝑓

CCS(V) as Function of Frequency II

Distance DUT - GR

1 µm

3 µm

20 µm

Simulation with variable

RSub only

RSub



2𝜋𝑓

CCS(V) as Function of Frequency III

Simulation with

RSub + CSub

RSub

CSub

CCS

[fF]

RSub

[Ω]

CSub

[fF]

1u

5.50

500 120

3u 750 50

20u 2500 33



2𝜋𝑓

CCS(V) as Function of Frequency IV

Simulation with

RSub + Csub + Rsub_2

Rsub

Csub

CCS

[fF]

RSub

[Ω]

Csub

[fF]

Rsub_2

[Ω]

1u

5.50

560 95 100

3u 820 42 140

20u 2600 31 110

RSub_2


• IHP bipolar technology SG13G2 (AE = 0.12x0.95 µm²)

• HBT variants with emitter numbers 1 – 8

• Constant distance HBT active collector to guard ring (2 µm)

Substrate Network for SG13G2 I

4Nx = 1 Nx = 4 Nx = 8

2 µm


Substrate Network for SG13G2 II

Nx = 1 Nx = 4 Nx = 8

Low ohmic

version

Rsub = 50/Nx

Drastic reduction

above 100GHz

VBE = 0.92V

VCE = 1.2V


Substrate Network for SG13G2 III

Nx = 1 Nx = 4 Nx = 8

Fitted Substrate Network

Rsub = 500 + 6000/Nx

Csub = 2.7fF + 2.84fFNx

Less reduction

above 200GHz

VBE = 0.92V

VCE = 1.2V


0 1 2 3 4 5 6 7 8 90

1000

2000

3000

4000

5000

6000

RS

ub

[ ]

Nx

• Scaling of substrate resistance and capacitance

Substrate Network for SG13G2 IV

0 1 2 3 4 5 6 7 8 90

2

4

6

8

10

CC

S [ fF

]

Nx

0

5

10

15

20

25

30

CSub [ fF

]


• Variation of substrate resistance and capacitance

• The strong differences in power gain of the Nx=1 and Nx=8 devices are not

caused by the substrate network.

• RSub in actual HBT already very high RSubCSub optimization not necessary?

Substrate Network for SG13G2 V

Nx = 1

Nx = 8

CSub =

1fF…100fF

CSub =

1fF…100fF


Substrate Network for SG13G2 VI

Nx = 1 Nx = 4 Nx = 8

Introduction of RSub_2 = 100Ω

Better fit for f >10GHz

But worse fmax(f) !!!!!!!!!!!

Increased reduction above 200GHz VBE = 0.92V VCE = 1.2V

2 µm


SG13G2 - HICUM

Nx = 1 Nx = 4 Nx = 8

Parameters:

alit = 1

alqf = 0

Parameters:

rsu, csu

substrate coupling for 500ghz hbts - tu dresden...• 𝑓𝑚𝑎𝑥𝑓 for high frequencies as...

Documents