Tunable Properties of Hydrogenated Amorphous/Nanocrystalline Silicon Thin-Films for Enhanced MEMS Resonators Performance

Mouro, J.; Gualdino, A.; Chu, V.

doi:10.1109/jmems.2013.2286453

Cited by 9 publications

(10 citation statements)

References 35 publications

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“…An alternative approach is to use these analytical models to estimate certain mechanical properties of the thin-film, instead. This has been done in previous works (see [4,40] and [41]), where, for example, the curvature radius of a composite thin-film/compliant substrate is used to determine the residual stress of the thin-films, depending on the deposition conditions in a chemical vapor deposition system.…”

Section: Discussionmentioning

confidence: 99%

“…Intrinsic strain. Intrinsic strain, also known as residual strain, is common in thin-film materials deposited rapidly during microfabrication [40,41]. A rapid deposition, such as those obtained with thermal evaporation or sputtering, can lead to internal structures of the material far from equilibrium, caused by the presence of impurities, internal voids or atoms displaced from the position within the crystalline structure.…”

Section: Thermoelastic Strainmentioning

confidence: 99%

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Derivation of analytical expressions for the stress/strain distributions, bending plane and curvature radius in multilayer thin-film composites

Mouro¹,

Ferreira²,

Silva³

et al. 2021

J. Micromech. Microeng.

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Recent paradigms, such as smart cities/homes, Internet of Things or portable and implantable healthcare systems, require the use of flexible and conformal sensors that can be assembled to arbitrarily 3D complex shapes. A good set of simple and available models is of paramount importance to help designing and fabricating such devices. In this work, analytical expressions for the bending plane, the curvature radii and the stress/strain distributions of multilayer composite devices are derived for the cases of uniaxial and biaxial plane stress and plane strain and generalised plane strain. The analytical results are summarized, and two case-studies are analysed and compared with the help of these models: bilayer and trilayer hinges for self-assembled structures and rolled up flexible substrates with sensors on top. The dependence of the curvature radii and strain and stress distributions on several mechanical properties of the composite is assessed. The applicability of these models to support the design of flexible sensors, electronics or haptic devices is discussed and their practical limitations analysed.

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Section: Discussionmentioning

confidence: 99%

Section: Thermoelastic Strainmentioning

confidence: 99%

Derivation of analytical expressions for the stress/strain distributions, bending plane and curvature radius in multilayer thin-film composites

Mouro¹,

Ferreira²,

Silva³

et al. 2021

J. Micromech. Microeng.

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“…After the fabrication, the strips carrying the MEMS devices were mounted on a custom designed PCB for electrical addressing, by inserting the PI strip in the flexible printed circuit (FPC) connector (OMRON XF3C) along with a plastic spacer to ensure contact to the pads as this FPC connector was designed for 0.12 mm-thick flexible cables (see figure 1(c)). The devices were then placed in a vacuum chamber (the pressure can be controlled from 10 -5 to 760 Torr) and characterized at resonance using an optical setup described elsewhere [25,[30][31][32]. In these measurements, an AC voltage is applied to the MEMS structure and a DC voltage is applied to the bottom electrode in order to create the electrostatic actuation force.…”

Section: Measuring Resonance and Frequency Stabilitymentioning

confidence: 99%

“…Microresonators are one of the most frequently used MEMS devices, for applications in frequency filtering, timing, inertial sensing, mass and chemical sensing applications [2,19]. Microresonators are commonly fabricated on silicon substrates but in the last decades glass and polymer substrates have received increasingly attention [4,7,[20][21][22][23][24][25][26][27]. In particular, Hao Jin et al worked in surface acoustic wave resonators (SAW) [20] and film bulk acoustic resonators (FBARs) [21] on flexible polymer substrates, both 100 μm thick PET and PI, and also explored using PI as a support layer for fabricating FBARs in other substrates, such as paper and glass [22].…”

Section: Introductionmentioning

confidence: 99%

“…Thin-film hydrogenated amorphous silicon (a-Si:H) can be deposited at low temperatures (100 °C) on large-area or lowcost substrates (glass, plastic), allowing the fabrication of thinfilm transistors (TFTs), photodetectors and MEMS in processes compatible with CMOS technology [4,24,25,27]. Recently, the first a-Si:H resonators on 10 μm-thick PI were successfully fabricated by our group [28].…”

Section: Introductionmentioning

confidence: 99%

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Fabrication and characterization of thin-film silicon resonators on 10 $\boldsymbol{{\mu}}$m-thick polyimide substrates

Pestana¹,

Pinto²,

Dias³

et al. 2020

J. Micromech. Microeng.

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MEMS fabricated on polymer substrates can allow for a range of new applications that require bending or lightweight, unbreakable substrates. The surface micromachining of hydrogenated amorphous silicon resonators on 10 µm-thick flexible polyimide substrates is presented. Clamped-clamped (bridges) and clamped-free (cantilevers) resonators are fabricated and characterized, exhibiting quality factors as high as 2.0 × 103 and natural resonance frequencies in the 104–106 Hz range. The deflection of an 80 µm long bridge was measured to be over 100 pm, using laser Doppler vibrometry. The electrical addressing of the devices was demonstrated to be reliable when bent to radii of curvature larger than 10 mm. The resonators on ultra-thin polymer are characterized using different actuation voltages and pressures, showing comparable performance to resonators on rigid (glass) substrates. However, the flexible substrate allows the relaxation of the residual stress of the structural film in clamped-clamped structures, lowering the resonance frequency. Resonators on PI were found to be suitable for mass-sensing applications, achieving a minimum frequency shift detectable Δfmin = 30 Hz which results in a calculated mass sensitivity of 25 pg in vacuum. Ultimately, the reliable performance of the resonators developed in this work make them good candidates for applications that require mass-sensing on ultra-thin, flexible substrates.

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Amorphous Silicon Self‐Rolling Micro Electromechanical Systems: From Residual Stress Control to Complex 3D Structures

2019

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In surface micromachining, the control of the residual stress of the films is crucial, as excessive stress can cause buckling, cracking, and peeling of the materials and fracture of the devices. However, the gradients of stress across the thickness of individual films or the stress mismatch in composite structural layers can be exploited to obtain highly complex 3D structures via self‐assembly, self‐bending, self‐positioning, or self‐rolling processes. Herein, the thin‐film residual stresses of amorphous silicon, TiW, AlSiCu, Cr, Au, and SiO2 are assessed using polymer substrates and tuned. Then, a stress‐mismatched bi‐layer of amorphous silicon (tensile) and TiW (compressive) is used in the fabrication of complex 3D self‐rolling micro electromechanical systems (MEMS) structures. The freestanding regions of the fabricated MEMS have a characteristic radius of curvature of ≈100 μm. Current‐induced thermal actuation of a suspended plate is demonstrated. The microfabrication process and materials used are compatible with standard cleanroom processing and with a variety of substrates. In the future, amorphous silicon photodiodes, photoconductors, or other semiconductor devices can be incorporated on complex MEMS fabricated by self‐rolling/self‐bending processes and applied to localized optical and electrical sensing.

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Tunable Properties of Hydrogenated Amorphous/Nanocrystalline Silicon Thin-Films for Enhanced MEMS Resonators Performance

Cited by 9 publications

References 35 publications

Derivation of analytical expressions for the stress/strain distributions, bending plane and curvature radius in multilayer thin-film composites

Derivation of analytical expressions for the stress/strain distributions, bending plane and curvature radius in multilayer thin-film composites

Fabrication and characterization of thin-film silicon resonators on 10 $\boldsymbol{{\mu}}$m-thick polyimide substrates

Amorphous Silicon Self‐Rolling Micro Electromechanical Systems: From Residual Stress Control to Complex 3D Structures

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