Silicon carbide for RF MEMS

Melzak, J. M.

doi:10.1109/mwsym.2003.1210450

Cited by 23 publications

(16 citation statements)

References 11 publications

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“…SiC is recognized for its superior mechanical, electrical and chemical properties, making it a good choice for applications in the harsh environments of these applications [1]. It is a semiconductor with a wide band gap, high acoustic velocity, high thermal conductivity, high electrical breakdown strength, and low chemical reactivity [2]. These characteristics also make it difficult to fabricate MEMS devices [3].…”

Section: Introductionsupporting

confidence: 70%

Detection of Residual Stress in Silicon Carbide MEMS by μ-Raman Spectroscopy

2005

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Micro-Raman (μ-Raman) spectroscopy is used to measure residual stress in singlecrystal, 6H-silicon carbide (SiC) used in micro-electro-mechanical-systems (MEMS) devices. These structures are bulk micro-machined by back etching a 250-μm-thick, single-crystal 6H-SiC wafer (p-type, 7 Ω-cm, 3.5º off-axis) to form a 50-μm thick diaphragm. A Wheatstone bridge, patterned of piezoresistive elements, is formed across the membrane from a 5-μm, 6H-SiC (n-type, doped 3.8 x 10 18 cm -3 ) epilayer; the output of the bridge is proportional to the flexure of the MEMS diaphragm. For these samples, the μ-Raman spectroscopy is performed using a Renishaw InVia Raman spectrometer with an argon-ion excitation source (λ = 514.5 nm, hν = 2.41 eV) with an approximate 1-μm 2 spot size through the 50X objective. By employing an incorporated piezoelectric stage with submicron positioning capabilities along with the Raman spectral acquisition, spatial scans are performed to reveal areas in the MEMS structures that contain residual stress. Shifts in the transverse optical (TO) Stokes peaks of up to 2 cm -1 along the edge of the diaphragm and through the piezoresistors indicate significant material strain induced by the MEMS fabrication process.The phonon deformation potential is measured to quantify the material stress as a function of the shift in the Raman peak position. The line center of the TO Stokes peak is shifted by applying a uniform stress to the sample and monitoring the applied stress using a strain gauge, while the μ-Raman spectrum is being measured. A spectral analysis code tracks the shift of the Raman peak position with respect to the line center of the Rayleigh peak to account for any thermal drift of the spectrometer during the time of the area scan.

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Section: Introductionsupporting

confidence: 70%

Detection of Residual Stress in Silicon Carbide MEMS by μ-Raman Spectroscopy

2005

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“…The nominal frequency is taken to be the highest frequency measured for the resonator and is hence associated with the lowest bias voltage. Shorter devices have lower sensitivity to the bias voltage because of their higher mechanical stiffness, which becomes dominant in relation to the electrical spring constant, as predicted by (13). Accordingly, the 32-μm-long resonator requires a prohibitively high voltage to reach a tuning range comparable with that of the longer beams.…”

Section: B Transfer Function Characteristicsmentioning

confidence: 99%

“…Equation (13) indicates that the tuning range deteriorates as the resonator stiffness increases, suggesting that electrostatic tuning ranges for high-frequency resonators are limited. This is illustrated in [3] and [31], where the tuning range of an 8-MHz beam resonator is of 9.4%, whereas that of a stiffer 193-MHz disk resonator is of 0.01%.…”

Section: Electrostatic Tuningmentioning

confidence: 99%

“…Notably, silicon carbide (SiC) is known to have superior mechanical properties compared with those of silicon. The mechanical properties of SiC are discussed in detail in [11]- [13]. Additionally, studies in [14]- [16] suggest that SiC-based MEMS devices are expected to exhibit a superior performance in many respects, e.g., aging, ruggedness, and, thus, reliability, as compared with those based on other well-known materials such as silicon.…”

Section: Introductionmentioning

confidence: 99%

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Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part II: Beam Resonators for MEMS Above IC

Nabki

Cicek

Dusatko

et al. 2011

J. Microelectromech. Syst.

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Microelectromechanical beam resonators and arrays are fabricated using a custom low-temperature complementarymetal-oxide-semiconductor-compatible silicon carbide microfabrication process, detailed in Part I of this paper. Theoretical aspects are presented with modal analysis and numerical methods. Measurements of the resonant frequency, the quality factor, the transmission, and the tuning characteristics are presented for different device types and dimensions. Trends are analyzed, and performance metrics dependences are investigated. A tuning method based on integrated heaters is introduced and tested, yielding a very desirable constant insertion-loss tuning and a wide tuning range. Quality factors of up to 1493 and resonant frequencies of up to 26.2 MHz are demonstrated. Both the Young's modulus and the residual stress of the SiC film are extracted (261 GPa and < ±30 MPa, respectively), and favorably compare to values reported for polysilicon. [2010-0235] Index Terms-Micromechanical resonators, microelectromechanical systems (MEMS), resonator arrays, silicon carbide (SiC), surface micromachining, thermal tuning.

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“…SiC has several advantages for HT applications ( [5] contains over 1000 references), and these advantages apply to certain MEMS applications [6], [7]. Its high stiffness (roughly three times that of polysilicon) makes it a good candidate for the high Q required in RF microdevices.…”

Section: Introductionmentioning

confidence: 99%

Fracture Strength of Single-Crystal Silicon Carbide Microspecimens at 24 $^{\circ}\hbox{C}$ and 1000 $^{\circ}\hbox{C}$

Sharpe

Beheim

Evans

et al. 2008

J. Microelectromech. Syst.

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Three shapes of silicon carbide tensile specimens were tested-curved with a low stress-concentration factor and straight with a circular hole or an elliptical hole. The nominal thickness was 125 µm with a net section that is 100-µm wide; the overall length of these microspecimens was 3.1 mm. They were fabricated by an improved version of deep reactive ion etching, which produced specimens with smooth sidewalls and cross sections having a slightly trapezoidal shape that was exaggerated inside the holes. The novel test setup used a vertical load train extending into a resistance furnace. The specimens had wedge-shaped ends which fit into ceramic grips. The fixed grip was mounted on a ceramic post, and the movable grip was connected to a load cell and actuator outside the furnace with a ceramic-encased nichrome wire. The same arrangement was used for tests at 24 • C and at 1000 • C. The strengths of the curved specimens for two batches of material (made with slightly different processes) were 0.66 ± 0.12 and 0.45 ± 0.20 GPa, respectively, at 24 • C with identical values at 1000 • C. The fracture strengths of the circular-hole and elliptical-hole specimens (computed from the stress-concentration factors and measured loads at failure) were approximately 1.2 GPa with slight decreases at the higher temperature. Fractographic examinations showed failures initiating on the surface-primarily at corners. Weibull predictions of fracture strengths for the hole specimens based on the properties of the curved specimens were reasonably effective for the circular holes but not for the elliptical holes.[2007-0057]

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Silicon carbide for RF MEMS

Cited by 23 publications

References 11 publications

Detection of Residual Stress in Silicon Carbide MEMS by μ-Raman Spectroscopy

Detection of Residual Stress in Silicon Carbide MEMS by μ-Raman Spectroscopy

Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part II: Beam Resonators for MEMS Above IC

Fracture Strength of Single-Crystal Silicon Carbide Microspecimens at 24 $^{\circ}\hbox{C}$ and 1000 $^{\circ}\hbox{C}$

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