PME5230 Midterm Presentation PME5230 Midterm Presentation 1

Temperature measurement and comTemperature measurement and compensation based on two vibrating mpensation based on two vibrating modes of a bulk acoustic mode microrodes of a bulk acoustic mode micror

esonator esonator

Teacher Teacher ： ： Cheng-Hsien Liu RReportereporter ：： Chien Thanh NguyenChien Thanh Nguyen

DateDate ：： 2008.4.162008.4.16

M.Koskenvuori1, V.Kaajakri2, T.Mattila and I. Tittonen1

1. Micro and Nanosciences laboratory and Center for New Materials, Helsinki University of Technology,Finland

2. VTT – Technical Research Center of Finland, Finland

MEMS 2008, Tucson, AZ, USA, January 13-17, 2008

PME5230 Midterm Presentation PME5230 Midterm Presentation 2

OutlineOutline Introduction Device Method Measurement results Discussion Conclusion

PME5230 Midterm Presentation PME5230 Midterm Presentation 3

IntroductionIntroduction

Temperature induced drift

MEMS resonator

Compensated electronicallyMaterial compensation SiO2

, Al2O3

PME5230 Midterm Presentation PME5230 Midterm Presentation 4

DeviceDevice

Single crystal silicon, square-extensional bulk-acoustic-mode resonator (SE-BAW)

Fundamental mode of vibration

Lame’ Mode

Square-extension mode

PME5230 Midterm Presentation PME5230 Midterm Presentation 5

MethodMethodDetermine temperature coefficients of the frequency of two mode

α1= ((df/f)/dT)lame= -22.3 ppm/K

α2 = ((df/f)/dT)SE = -27.3 ppm/K

PME5230 Midterm Presentation PME5230 Midterm Presentation 6

MethodMethod

(1)

(2)

PME5230 Midterm Presentation PME5230 Midterm Presentation 7

Measurement ResultsExperiment setup

1) Pt-100 sensor next to resonator chip

2) Resonator as a thermometer itself

PME5230 Midterm Presentation PME5230 Midterm Presentation 8

PT-100: frequency error: 15ppm

PT-100: compensation error df/f > 2 ppm

Resonator thermometer: compensated df/f < 1 ppm

PME5230 Midterm Presentation PME5230 Midterm Presentation 9

PME5230 Midterm Presentation PME5230 Midterm Presentation 10

DiscussionDiscussionDisadvantage:

1) A very accurate frequency measurement is needed

2) The beat frequency of the two modes is fairly high reducing the sensitivity

3) Any mixing products of the two excited modes will degenerate the reference oscillator noise performance

PME5230 Midterm Presentation PME5230 Midterm Presentation 11

ConclusionConclusionA resonator can be used as a thermometer by measuring the frequency change of the Lame- and SE- mode Temperature induced frequency shift can be compensated to better Provide a cost effective way to obtain crystal oscillator (TCXO) performance with inexpensive silicon resonator.

PME5230 Midterm Presentation PME5230 Midterm Presentation 12

Thank you for your attention!Thank you for your attention!

PME5230 Midterm Presentation PME5230 Midterm Presentation 13

ReferenceReferenceCMOS-compatible dual-resonator MEMS temperature se

nsor with mili-degree accuracyC.M. Jha, G. BAhl, R. Melamud, S.A. Chandorkar, M.A. Hopcroft, B. Kim, M. A

garwwal, J. Salvia, H. Mehta and T.W. Keny(transducer 2007)