Polysilicon resonant microbeam technology for high performance sensor applications

Guckel, H.; Rypstat, C.; Nesnidal, M.; Zook, J. D.; Burns, D.W.; Arch, D.K.

doi:10.1109/solsen.1992.228303

Cited by 27 publications

(8 citation statements)

References 3 publications

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“…Although the devices are also temperature dependent, the temperature coefficient of frequency is only -10 ppm/"C and cannot account for the large magnitude of the shift. The downward shift in frequency is much greater than that reported for other polysilicon resonators [21]. However in this case, the amplitude of motion was very large.…”

Section: Methodscontrasting

confidence: 57%

Polysilicon hollow beam lateral resonators

Judy¹,

Howe²

[1993] Proceedings IEEE Micro Electro Mechanical Systems

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This paper reports the first microfabrication of hollow polysilicon beams. Arrays of lateral resonators are designed, processed, and tested with resonant frequencies from 8 kHz to 0.5 MHz. The quality factor as a function of pressure of the hollow beam resonators is compared with solid beam resonators, and values as high as 34,000 are obtained in vacuum. The hollow beam resonators are verified with theory and compared to resonators with solid cross sections. I. INTRODUCTIOKIn recent years, polysilicon surface micromachining has been used to fabricate vertical and lateral resonators [l, 21, as well as a variety of other flexure-suspended microstructures [3, 41. A feature of this simple process is that the mechanical elements are defined by etching a single LPCVD polysilicon structural layer, which is usually around t = 2 pm in thickness. A typical minimum linewidth is W = 1 -2 p m , assuming optical lithography, reactive ion etching, and a photoresist etch mask. The minimum-geometry polysilicon beam therefore has an aspect ratio t / W = 1 -2 and consists of solid polysilicon, which is a major constraint on the mechanical design of the flexural suspension and the rigid elements of the microstructure. This paper reports on the fabrication of hollow micromeclianical structures, which have cross sections shown in Figure 1. The reasons for investigating hollow cross section microstructures are twofold. First, by making the entire structure hollow the stiffness-tc-mass ratio of the flexures increases, which increases the resonant frequency. A high frequency, high Q oscillator will have niany potential applicat,ions, such as in resonant microsensors, on-chip clocks, and niicromechanical filters [5, 61. The design of lateral resonators with solid suspensions becomes difficult for frequen- Figure 1: Perspective drawing of hollow beam lateral resonator. The entire structure is hollow, not just the suspension beams.The second reason for investigating hollow beams is that the devices are more sensitive to mass loading and to axial loading, simply because the masses and stiffnesses of the resonators are lower than for the solid cross section devices. In addition, the surface to volume ratio of the hollow devices is very large, indicating that surface effects, such as etchant attack of the polysilicon, might be observable.We first describe the fabrication process sequence required to fabricate the polysilicon hollow beam devices. Next, the theory behind these resonators is discussed, including the nonlinearities of the mechanical flexure and electrostatic comb drive as well as a comparison of hollow and solid beam devices. Experimental results that agree with the theory are then presented. Finally, the advantages and future applications of hollow beam devices are discussed. FABRICATIONcies over a few MHz, because the beam lengths required are very short, constraining the shuttle to small oscillations in order to maintain linearity. Calculations and experiments show that a hollow lateral resonator can have approximately 2-4X th...

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Section: Methodscontrasting

confidence: 57%

Polysilicon hollow beam lateral resonators

Judy¹,

Howe²

[1993] Proceedings IEEE Micro Electro Mechanical Systems

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“…This provides not only the immunity to any amplitude measurement errors but also quasi-digital outputs to simplify the interfacing with digital systems. Some early micromachined resonant accelerometers are based on polysilicon (Burns et al 1996, Chang et al 1990, Guckel et al 1992, Roessig et al 1997, Seshia et al 2002. Quartz, single crystal silicon (SCS), and polysilicon are the common materials for resonators.…”

Section: Resonant Accelerometersmentioning

confidence: 99%

“…In the late 1980s and early 1990s, the use of polysilicon as an accelerometer mechanical spring and mass structure was investigated by numerous university groups, such as the University of California at Berkeley (UC-Berkeley) (Boser andHowe 1995, Lu et al 1995), the University of Wisconsin (Guckel et al 1992), and the University of Berlin (Fricke and Obermeier 1993). Polysilicon is a common material used in silicon gate complementary metal oxide semiconductor (CMOS) transistors and therefore is compatible with IC processing.…”

Section: Introductionmentioning

confidence: 99%

Accelerometers

Xie

Fedder

Sulouff

2008

Comprehensive Microsystems

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“…The fine-grained, undoped polysilicon developed by H. Guckel and his group at the University of Wisconsin is deposited at 575 C and then annealed to produce a low residual strain material [71], [72]. Conducting regions in this otherwise high-resistivity polysilicon are formed by ion implantation [73].…”

Section: A Materials Properties 1) Residual Stressmentioning

confidence: 99%

“…Quality factors of 50 000-100 000 in vacuum are typical of polysilicon microresonators [4], [72], [73], [86]. Electrostatically driven polysilicon resonant structures encapsulated in thin-film vacuum chambers have been shown to possess shortterm stability better than 0.02 Hz for kHz [27].…”

Section: B Microstructure Dimensionsmentioning

confidence: 99%