Mechanical strengthening of silicon torsion bar of MEMS scanning mirror by hydrogen anneal

Hajika, R.; Yoshida, Shinya; Makishi, Wataru; Kanamori, Yoshiaki; Tanaka, Shuji; Esashi, Masayoshi

doi:10.1109/memsys.2013.6474269

Cited by 9 publications

(11 citation statements)

References 5 publications

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“…Recent literature has shown that the presence of surface scallops severely limits the fracture strength of SCS [19]. This implies that such surface defects may severely limit the fatigue lifetime of a SCS device, and that complete surface smoothing with hydrogen annealing, such as from 'epi-seal' encapsulation, leads to a fatigue-free device.…”

Section: Summary Of Resultsmentioning

confidence: 99%

“…sidewall 'scallops') as another possible surface-defect-based fatigue mechanism. The presence of such scallops severely limits the mechanical strength of SCS [19]. Furthermore, it has been shown that the crack length needed to initiate fracture could indeed be comparable to the surface features caused by scallops, leading to another possible fatigue mechanism [20].…”

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confidence: 99%

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Fatigue Experiments on Single Crystal Silicon in an Oxygen-Free Environment

Hong

Yoneoka²,

Messana³

et al. 2015

J. Microelectromech. Syst.

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The fatigue lifetime of single crystal silicon (SCS) was characterized in an environment free of oxygen, humidity, and organics. Long-term (>10 10 Hz) fatigue experiments performed with smooth-walled SCS devices showed no signs of fatigue damage up to 7.5 GPa. In contrast, experiments using SCS devices with a silicon dioxide (SiO 2 ) coating and rough sidewalls due to scalloping from deep reactive ion etching exhibited fatigue drift at 2.7 GPa and suffered from short-term (< 10 10 Hz) fatigue failure at stress levels >3 GPa. In these SCS-SiO 2 experiments, the initiation of fracture occurs in the SiO 2 layer. It is concluded that fatigue in this case is likely attributed to a subcritical cracking mechanism; not reactionlayer nor dislocation related. A cross-comparison with other works from literature is developed to show that packaging a pristine device in an inert environment is necessary in order to operate devices at high-stress levels.[2013-0267]

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Section: Summary Of Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Fatigue Experiments on Single Crystal Silicon in an Oxygen-Free Environment

Hong

Yoneoka²,

Messana³

et al. 2015

J. Microelectromech. Syst.

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show abstract

“…Surface modification processes have been attempted to improve the fracture properties of SCS structures by annealing in a hydrogen environment 47,48 or by transient laser annealing 49 . However, careful comparison should be made because such annealing induces changes in material conditions such as the DRIE process alteration, not just in the surface morphology.…”

Section: Comparison With Previous Specimensmentioning

confidence: 99%

“…These observations suggest that the surface scallops formed by DRIE cannot be regarded directly as an initial crack for brittle fracture. Including other experimental results 48,51 exhibiting the improvement effects of surface treatments, further detailed comparisons will be required. Because the strength evaluation methods (fracture or fatigue) give only phenomenological results, additional assistance from microscopic technologies will be strongly desired to further elucidate the surface condition effects.…”

Section: Comparison With Previous Specimensmentioning

confidence: 99%

Crystal orientation-dependent fatigue characteristics in micrometer-sized single-crystal silicon

Ikehara

Tsuchiya

2016

Microsyst Nanoeng

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Repetitive bending fatigue tests were performed using five types of single-crystal silicon specimens with different crystal orientations fabricated from {100} and {110} wafers. Fatigue lifetimes in a wide range between 10 0 and 10 10 were obtained using fan-shaped resonator test devices. Fracture surface observation via scanning electron microscope (SEM) revealed that the {111} plane was the primary fracture plane. The crack propagation exponent n was estimated to be 27, which was independent of the crystal orientation and dopant concentration; however, it was dependent on the surface conditions of the etched sidewall. The fatigue strengths relative to the deflection angle were orientation dependent, and the ratios of the factors obtained ranged from 0.86 to 1.25. The strength factors were compared with those obtained from finite element method stress analyses. The calculated stress distributions showed strong orientation dependence, which was well-explained by the elastic anisotropy. The comparison of the strength factors suggested that the first principal stress was a good criterion for fatigue fracture. We include comparisons with specimens tested in our previous report and address the tensile strength, initial crack length, volume effect, and effects of surface roughness such as scallops.

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“…There are various methods to improve the surface roughness and strength of silicon microstructures, such as anisotropic wet etching of silicon [4], hydrogen annealing [5], oxidation [6], and laser ablation [7]. Among them, smoothing using oxidation is simple and easy to implement to standard fabrication process.…”

Section: Introductionmentioning

confidence: 99%

Fracture behavior of single crystal silicon with thermal oxide layer

Tsuchiya

Miyamoto

Sugano

et al. 2016

Engineering Fracture Mechanics

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This paper reports on the effect of oxidation on fracture behavior of single crystal silicon (SCS). SCS specimens were fabricated from (100) silicon-on-insulator wafer with 5-μm-thick device layer and oxide layer were thermally grown. Quasi-static tensile testing of as-fabricated, oxidized and oxidized layer removed specimens was performed. The fracture origin location transited from the surface to silicon/oxide interface and inside of silicon. The transition may be caused by surface smoothing, thickening oxide layer and formation of oxide precipitation defects in silicon during oxidation. The radius of the oxide precipitation defects was estimated, which is well agreed with the fracture-initiating crack sizes.

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Mechanical strengthening of silicon torsion bar of MEMS scanning mirror by hydrogen anneal

Cited by 9 publications

References 5 publications

Fatigue Experiments on Single Crystal Silicon in an Oxygen-Free Environment

Fatigue Experiments on Single Crystal Silicon in an Oxygen-Free Environment

Crystal orientation-dependent fatigue characteristics in micrometer-sized single-crystal silicon

Fracture behavior of single crystal silicon with thermal oxide layer

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