IHP

Im T

echnologiepark 2515236 F

rankfurt (Oder)

Germ

any

!

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Different S

piral Inductor

Layouts-T

heir Influence on Q

, fSR and S

pice Param

eters

Erzgräber, H

eide

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Optim

um design of spiral inductors w

ith respect to

• M

aximum

Quality F

actor Q

• M

inimum

area consumption (A

sp)

• S

ufficiently high self-resonant frequency (fS

R )

Motivation

!

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One spiral

Do = 410 µm

Tw

o conv. stacked spirals

D

o = 325 µmA

new stacked spiral w

inding doubles fS

R.

0.00.4

0.81.2

0 1 2 3 4

ρρρ ρS

i = 15 ΩΩΩ Ωcm

L = 92 - 95 nHnorm

al isolation

newstacked

conv.stacked

onespiral

Quality Factor

Frequency (G

Hz)

Quality F

actor versus Frequency

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Cox2

Cox1

RS

i2C

Si2

CS

i1

CS

RS

LS

RS

i1

•••

•

RLC

Loop 2

RLC

Loop 1

• Typical w

inding:

Lines in close proximity are nearly

equipotential !

CS is sm

all

• RLC

loop 1 is dominant

fSR = f (layout, technology)

• Winding w

ith strongly increased C

s or spiral on

insulating substrates C

S = C

iw + C

cross C

iw = f( lsp, tM , 1/S

, W)

Ccross = f(W

, Wup , N

, tIsp-up )

• RLC

loop 2 is

dominant

fS

R = f(layout, tM , tIsp

-up )

Silicon technology:

two

RLC

loops determine f

SR

.

Cox2

Cox1

RS

i2C

Si2

CS

i1

CS

RS

LS

RS

i1

•••

•

Lumped E

lement C

ircuit Model

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123

4

1234

Ciw

CM

IM

Conventional stacked w

inding:increased ac potential

differencesN

ew stacked w

inding:sm

all ac potential differences

InOut

12

34

56

M3

M2

M1

S

InOut

12

45

6

Given by

technology

Spacing

chosen bylayout

CM

IM

Ciw

Stacked S

pirals

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Quality F

actor versus Frequency

01

23

45

67

0 1 2 3 4 5 6 7

L = 15 nH

ABC

Quality Factor

Frequency (G

Hz)

Type of

Spiral W

indingfS

R

(GH

z)Q

(2 GH

z)(conv. Q

-extraction)

A2 spirals inseriesconvent.w

inding

2.120.31

B2 spirals inseriesneww

inding

5.455.94

C1 spiral

6.76.3

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Tw

o Spirals

in Series

- Conventional W

inding

01

23

4

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Frequency (G

Hz)

Mag Y11

-90

-60

-30

0 30 60 90

2 spirals in series

fSR

L06 (15 nH)

Port 2

Port 1

Ang Y11

• Conventional w

inding:

Large capacitance between

the stacked spirals

Cs = 218

fF

• Low self-resonant frequency

• Sm

all influence of substrate

resistance - Cs is dom

inant !

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Conventional Inductor

- Only one S

piral

02

46

810

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Frequency (G

Hz)

Mag Y11

-90

-60

-30

0 30 60 90

1 spiral in metal 4

L05st (15 nH)

Port 2

Port 1

Ang Y11

• Higher self- resonant frequency

Cs only 15.4

fF

• Increased spiral area (70 %)

• No sym

metry for P

orts1 and 2

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Inductor w

ith N

ew T

ype of S

pirals in Series

02

46

8

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Frequency (G

Hz)

Mag Y11, Y22

-90

-60

-30

0 30 60 90

2 spirals in series

L05 (15 nH)

Port 2

Port 1

Ang Y11, Y22

• Decreased capacitance betw

een

the two stacked spirals:

Cs only 42

fF

fS

R about doubled

• Nearly sym

metry betw

een both

ports

• Asp decreased by 40 %

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Tw

o Spirals

in Series - Influence

of Substrate D

oping

02

46

0 2 4 6L = 15 nH

Type B

Type A

p+ S

i (0.01 ΩΩΩ Ωcm

)

p- S

i and p+ epi-S

i

p- S

i (50 ΩΩΩ Ωcm

)

p+ S

i

p- S

i and p+ epi S

i

p- S

i

Quality Factor

Frequency (G

Hz)

Type A

winding :

Cs is dom

inant -substrate doping hasonly sm

all influence.

Type B

winding:

Cs is sm

all -now

fSR is a strong

function of substratedoping.

tox : 3.3 µm

upper spiral:

tM4 : 2 µm

lower spiral:

tM3 + tM

2 : 1.2 µm

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S

umm

ary and Conclusions

• P

arasitics, depending on the type of spiral winding, reduce

fSR ,

lim

it the operating frequency and the capacitive load.

• W

e propose to improve

fSR by m

inimizing the ac potential

differences between lines in close proxim

ity.

• Based on this principle

a new w

inding for stacked spirals is investigated w

hich nearly doubles fS

R .

• T

his allows a higher operating frequency, and / or a higher

capacitive load in circuit applications.

• Besides, nearly sym

metric S

pice Param

eters are obtained for both ports.

• N

ow, w

ithout dominance of second order effects, better technological

conditions can further improve the inductor perform

ance.

+,-+./01234 546 7089:;<=>= <?@A:9 3;BC :DEFG0 :HI0 :.9 3J

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Characteristic Inductor D

ata

Type of Inductor

Ls(nH)

tsp_sub(µm

)R

s( ΩΩΩ Ω

)W(µm

)S(µm

)D

out(µm

)

A2 spirals in series1 spiral in m

etal 4,1 spiral in M

3 parallel M2

conventional winding

153...3.3

138

2192

B2 spirals in series1 spiral in m

etal 4,1 spiral in M

3 parallel M2

new w

inding

14.73...3.3

158

2192

C1 spiral in m

etal 414.6

≈≈≈ ≈ 616

72

250

tsp_sub: thickness of isolation between spiral and silicon substrate

W : w

idth of metal track S

: spacing between turns

Dout: outer diam

eter of spiral

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0.00.4

0.81.2

1.62.0

0 1 2 3 4 5

L = 92 - 95 nH

0.01 ΩΩΩ Ωcm

ρρρ ρS

i = 15 ΩΩΩ Ωcm

newstacked

onespiral

conv.stacked

Quality Factor

Frequency (G

Hz)

Conventionally stacked:

• Large parasitic capacitance betw

een both spirals is dom

inant.• fS

R is strongly decreased.

• Low influence of im

proved isolation and substrate resistivity.

Spiral

8 µmburiedoxide

Improved Isolation