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MMICRONOVAICRONOVACentre for microCentre for micro-- and nanotechnologyand nanotechnology

RF-MEMS activities in Micronova

Mika Koskenvuori

[email protected] Research Institute

Research Highlights Seminar3.12.2004 Micronova – Helsinki University of Technology


What is MEMS?

MEMS = MicroElectroMechanicalSystem

Use fabrication methods learned from the IC-processing to fabricate (3D)mechanical structures


Outline

• Introduction and motivation• MEMS-based reference oscillator• Stability-issues• IC-electronics• Conclusions


Introduction

Motivation – Why MEMS?

Small size

Photo: Jyrki Kiihamäki


Introduction


Good performance•Low losses•Low power consumption•High stability

-10

-5

0

5

10

15

14758500 14758750 14759000 14759250 14759500 14759750 14760000Frequency [Hz]

S 21 [

dB

]

-140

-120

-100

-80

-60

-40

-20

0

20

Ph

ase

[Deg

85 Hz

3 dBQ=180 000


Introduction


Utilizes “standard” IC-manufacturing processes:•Mass production•Low price•Possibility to integrate


Introduction

Motivation

Source: http://www.inside-gsm.com


• Motivation• MEMS-based reference oscillator• Stability-issues• IC-electronics• Conclusions


MEMS-Based reference oscillator

Scaling

sizefr

1∝ fr ~ 1 GHzfr ~ 1 kHz fr ~ 100 kHz fr ~ 10 MHz

L~

10 c

m L~

1 m

m

L~

10 µ

m

L~

100

nm

MEMS NEMS

now future

• Typically coupling gets weaker as size is reduced• Dissipations are increased by reducing the size



Specifications

• High stability• Aging < 1ppm/year

• Low noise• Phase noise

• -130 dBc/Hz@1kHz• Noise to carrier

• -150 dBc/Hz-150dBc/Hz-130dBc/Hz

1kHz

1/fm3

1/fm1

L(fm)

fm0

1/fm0

SSB Phase Noise Spectrum


Outline



Long-term stability - Encapsulation process

Encapsulated sample


Long-term stability - Results Long-term stability - Results

Stability of resonance frequency:Vacuum encapsulated vs. open samples ( > 1 month)

0 200 400 600 800 1000-80

-70

-60

-50

-40

-30

-20

-10

0

10

0 200 400 600 800 10000

5

10

15

20

25

30

35

40

Time [h]

df/f

[ppm

] RH

[%]

Sample 1

Sample 2

Sample 3

Sample 4

Rel.Humidity

• All four samplesmeasuredsimultaneously

•Data temperaturecompensated

•Common bias-voltage (40V) on all the time

note correlation betweenRH and fr (open samples)

encapsulated samples

open samples

M. Koskenvuori et al. Sensors and Actuators A, 115 (2004)


Long-term stability - Results Long-term stability - Results

Detailed analysis of the vacuum-encapsulated samples

0 200 400 600 800 1000-6

-5

-4

-3

-2

-1

0

1

2

0 200 400 600 800 100030

40

50

60

70

80

90

100

Time [h]

df/f

[ppm

] T [°C

]

Sample 1

Sample 2

Temperature

Temperature cycle 1+30K (duration 8h)

Temperature cycle 2+30K (duration 4h)

Power-off (reboot)- amplifier- bias

Devices taken outside the chamber

M. Koskenvuori et al. Sensors and Actuators A, 115 (2004)



MEMS-resonator with IC-electronics

Vbias

buffer

In2

out

Out1

loop amplifier

VDD

gnd

In1

Gaincontrol

loop amplifier

Vbias

CPCP

out

buffer

CL = 10 pF

P. Rantakari et al. Transducers’05 (2005) - submitted



Simulated results

10-1 100 101 102 103 104 105 106

-140

-120

-100

-80

-60

-40

-20

fm [Hz]

SS

B p

hase

noi

se [d

Bc/

Hz]

P has e nois e a t gateP has e nois e a t output Design parameters:

Cp = 1pFro = 630kΩgm = 0.030 mSp = 117.5 ppm∆C = 18.5542 fFgm,buffer = 0.084 mSQL = 51040



MEMS-resonator

320 µm

Photo: Jyrki Kiihamäki



MEMS-resonator

12.93 12.931 12.932 12.933 12.934 12.935 12.936 12.937-30

-20

-10

0

10

20

30

Frequency [Hz]

S21

[dB

]

S 21

12.93 12.931 12.932 12.933 12.934 12.935 12.936 12.937

-150

-100

-50

0

Frequency [Hz]

Pha

se [D

egre

e]

20V

4V

[fF]560C0Stray capacitance[µA]150IMAXMaximum current

[mH]670LmMotional inductance[Ω]500RmMotional resistance[aF]230CmMotional capacitance[nm]180DTransducer gap

110 000Q0Unloaded Q-factor[MHz]12.933F0FrequencyUnitsValueSymbolParameter

[fF]560C0Stray capacitance[µA]150IMAXMaximum current

[mH]670LmMotional inductance[Ω]500RmMotional resistance[aF]230CmMotional capacitance[nm]180DTransducer gap

110 000Q0Unloaded Q-factor[MHz]12.933F0FrequencyUnitsValueSymbolParameter



IC-electronics

• STMicroelectronics process

–BiCMOS–0.25 µm–2.5 V



Loop-amplifier

1 0 5 1 0 6 1 0 7- 1 6 0

- 1 5 5

- 1 5 0

- 1 4 5

- 1 4 0

- 1 3 5

- 1 3 0

- 1 2 5

F r e q u e n c y [ H z ]

Noi

se [d

Bm

/Hz]

I n p u t R e d u c e d N o i s e o f d 5

1 . 51 . 61 . 71 . 81 . 92

1 0 3 1 0 4 1 0 5 1 0 6 1 0 7

- 2 0

- 1 0

0

1 0

2 0

3 0

4 0

F r e q u e n c y [ H z ]

Gai

n [d

B]

1 . 71 . 81 . 922 . 1

Frequency [Hz]

Gai

n [d

B]

Frequency [Hz]

Noi

se [d

Bm

/Hz]

24854992011087253

rout [kΩ]

29.9611.289272.250.929.8455.5208813.55.41.98.25141.046240161.85.88260.03318333.21.75.19393.0583138.555.41.64.43524.4184205.2582.11.5

Vn [nV/√ Hz]gm [uS]Pdc [uW]Idc [uA]Vb [V]

24854992011087253

rout [kΩ]

29.9611.289272.250.929.8455.5208813.55.41.98.25141.046240161.85.88260.03318333.21.75.19393.0583138.555.41.64.43524.4184205.2582.11.5

Vn [nV/√ Hz]gm [uS]Pdc [uW]Idc [uA]Vb [V]



MEMS-resonator with IC-electronics

P. Rantakari et al. Transducers’05 (2005) - submitted

-1000 -500 0 500 1000-150

-100

-50

0

Frequency[Hz]

PSD

[dB

m/H

z]

Agilent 89400 dynamic range: 120 dB

buffer noise

-1000 -500 0 500 1000-1000 -500 0 500 1000-150

-100

-50

0

-150

-100

-50

0

Frequency[Hz]

PSD

[dB

m/H

z]

Agilent 89400 dynamic range: 120 dB

buffer noise

Parameter Symbol Value UnitFrequency f 0 12.93 [MHz]Output level U out 300 [mVpp]

Power consumption P 240 [µW]Motional current i mot 25 [µA]Buffer noise V n 5.7 [nV/sqrt(Hz)]Noise floor C/N -144 [dBc/Hz]


Conclusion

Summary

• MEMS devices could offer an integrable alternative for discrete components in the future

• Stability of RF-MEMS devices was found to be sufficient for even GSM-specifications

• A micromechanical oscillator was demonstrated with MEMS-resonator and custom IC-electronics

•Low power consumption was demonstrated•Sufficient noise-floor was demonstrated•Sufficient phase-noise performance is expected

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