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This work presents a study of photostriction-based optical actuation in bilayer cantilevers made of silicon and germanium thin-films and follows previous work in this area on silicon cantilevers. This experimental and theoretical study examines the role of the silicon-germanium heterojunction in optical actuation. It is shown that the germanium layer dominates the mechanical response of the device, which can be exploited to achieve enhanced optical actuation in cantilevers. [ABSTRACT FROM AUTHOR]

This paper reports the development of a broadband highly reflective and structurally flat large-area 2-D subwavelength grating (SWG) reflector, based on a tensioned single-layer silicon metamaterial membrane. Rigorous coupled-wave analysis is adopted to design the metamaterial reflector, resulting in a wavelength range of 600 nm (1.9- $2.5~\mu \text{m}$) with >99% reflectivity, which represents the largest reported fractional bandwidth $\Delta \lambda /\lambda _{\mathrm {c}}$ of 27%. Effects of design parameter deviations on the SWG reflector reflectivity are studied, showing that the reflector design has good fabrication tolerances. A freestanding 2-mm dimension 2-D SWG reflector has been fabricated with high precision, and optical measurements indicate polarization-independent average reflectivity of 99% over the wavelength range of 1.91- $2.49~\mu \text{m}$ , which agrees well with the modeled result. This paper also, for the first time, examines the surface flatness characteristics of a suspended single-layer 2-D SWG reflector. With a tensile stress of 10 ± 5 MPa in the silicon grating membrane, the freestanding reflector achieves nanometer-scale surface flatness, which provides a significant advantage over multilayer DBRs requiring stress-balancing. Furthermore, a hyperspectral Fabry-Perot shortwave infrared filter based on a top suspended 2-D SWG reflector and a bottom 4-pair Si/SiO2 distributed Bragg reflector (DBR) has been experimentally demonstrated for the first time. The filter is measured to have a peak transmission of 80% with a narrow full-width at half-maximum (FWHM) of about 4 nm. This spectral resolution is one order of magnitude higher than that of other reported MEMS/DBR-based Fabry-Perot filters and is well-suited to highly demanding hyperspectral shortwave infrared imaging applications. [2022-0060] [ABSTRACT FROM AUTHOR]

Amorphous and polycrystalline silicon are commonly used as sacrificial layers in the surface micromachining of microelectromechanical systems (MEMS) devices, because they have high thickness uniformity over a large wafer area, and a similar coefficient of thermal expansion to suspended structural materials such as silicon nitride and silicon oxide. However, the low deposition rate of amorphous-silicon hinders its application in devices that require a suspension gap greater than several micrometres, and chemical stability can be an issue. This paper addresses these issues through the development of a high deposition rate hydrogenated amorphous silicon thin film process. We have demonstrated two unique processing regimes, which can support either a low or high temperature process. The low-temperature processes can be used to deposit silicon thin films at temperatures fromroom temperature up to 100°C, with deposition rates as high as 0.2 \mu \textm /min. The high-temperature recipes, deposited at temperatures at and above 200°C, have a slightly lower deposition rate of 0.14 \mu \textm /min, but are found to be chemically resistant to etching in positive photoresist developer. [2016-0273] [ABSTRACT FROM AUTHOR]

This paper reports on a MEMS tunable Fabry–Perot filter technology capable of achieving nanometer-scale optical flatness across a large mirror area of up to square centimeters without any extraneous stress management techniques. The device employs a single-layer tensile silicon or germanium membrane for the suspended top mirror. Optical characterization of the fabricated single-membrane-based tunable filters for the SWIR, MWIR, and LWIR is presented. The fabricated 1000-$\mu$m dimension Si-membrane-based SWIR and MWIR filters are demonstrated with a wavelength tuning range of 1.77–2.42 and 4.1–4.9 $\mu$m, respectively, while the fabricated 200-$\mu$m-dimension Ge-membrane-based LWIR filter is demonstrated with a wavelength tuning range of 8.5–11.46 $\mu$m. All these filters are shown to achieve transmission characteristics that exceed the optical requirements for multispectral imaging applications. A large-area 1-cm dimension Si membrane-based SWIR tunable Fabry–Perot filter for multispectral imaging is demonstrated as a proof-of-concept, showing an excellent surface flatness in the order of 25 nm and an excellent optical uniformity with transmission peak wavelength variability less than 3% across the entire 1-cm dimension optical imaging area. In addition, the optical transmission behavior of the Fabry–Perot filters based on three-layer Si or Ge-based air-spaced DBRs for SWIR, MWIR, and LWIR is modeled, demonstrating that these filters can achieve a fine spectral resolution of several tens of nanometers suitable for hyperspectral imaging applications. [ABSTRACT FROM PUBLISHER]

This paper presents a study of the effects of stress and thermal expansion of inductively coupled plasma enhanced chemical vapor deposited (ICPCVD) amorphous Si thin films on low-temperature microelectromechanical systems test structures. Experimental data were used in conjunction with finite-element modeling (FEM) to predict deformation in simple microstructures across a wide temperature range from 85 to 300 K. Temperature dependence of residual stress and the coefficient of thermal expansion (CTE) of ICPCVD Si thin films was investigated by characterizing the curvature of bilayer thin-film samples through the use of optical profilometry at low temperature. Extracted parameters were used in an FEM package to confirm the experimental results by correlating with observed deformation of fabricated test structures. It is demonstrated that the experimentally determined CTE enables accurate modeling of the mechanical behavior of thin-film microstructures across a wide range of temperatures. [2015-0175] [ABSTRACT FROM PUBLISHER]

We present the design, fabrication, and optical characterization of silicon-air-silicon-based distributed Bragg reflectors, or quarter wavelength mirrors, in sizes ranging from 200 \mu \textm\times 200~\mu \textm to 5 mm $\times$ 5 mm. Such mirrors can be used in conjunction with either single-element photodetectors or large-area focal plane arrays to realize tunable multispectral sensors or adaptive focal plane arrays from the short-wave infrared wavelength ranges (1500–3000 nm) to mid-wave infrared wavelength (3000–6000 nm) ranges. Surface optical profile measurements indicate a flatness of the order of 20–30 nm in the fabricated structures across several millimetres. Single point spectral measurements on devices show excellent agreement with simulated optical models. The fabricated distributed Bragg reflectors show $\sim 94$ % reflectivity, which is in close agreement with theoretical reflectivity. The demonstrated high reflectivity across a wide wavelength range renders them suitable as broadband reflectors. Finally, we present optical transmittance modeling results for Fabry-Pérot filters based on these distributed Bragg reflectors. [2015-0161] [ABSTRACT FROM AUTHOR]

In this paper, we present the optimization of optical and mechanical properties of inductively coupled plasma chemical vapor deposited (ICPCVD) amorphous silicon thin films for fabrication of high-quality optical microelectromechanical systems-based devices operating from visible to short-wave infrared wavelengths (450–3000 nm). Our results indicate that, at relatively high deposition temperatures for plasma CVD, a decrease in the ICP power results in films with lower tensile stress, higher refractive index, and lower extinction coefficient. We show that hydrogen concentration alone is not a sufficient parameter for controlling optical and mechanical quality of the films. In particular, both the hydrogen concentration and the hydrogen-silicon bonding nature together play a vital role in determining the optical and the mechanical quality of the silicon thin films. As a demonstration vehicle, three layer silicon-silicon oxide-silicon-based distributed Bragg reflectors were fabricated for the visible (500–700 nm), near infrared (700–1000 nm), and short-wave infrared (2000–3000 nm) wavelength ranges using an optimized silicon fabrication recipe. The measured optical transmission spectra show close to 90% peak reflectivity. Finally, stress optimization was evaluated by fabricating 270-\mu \mathrm m diameter circular suspended silicon membranes, which demonstrate a flatness variation on the order of $<6$ nm across the entire lateral dimension. [2015-0029] [ABSTRACT FROM PUBLISHER]

We present the design, fabrication, and optical and mechanical characterization of silicon-/silicon-oxide-based optical filters and distributed Bragg reflectors in sizes ranging from 500 ~\mu m \times 500 ~\mu m to 5~mm \times 5~mm . They are designed to be used in conjunction with either single-element photodetectors or large-area focal plane arrays to realize tunable multispectral sensors or adaptive focal plane arrays in the shortwave infrared wavelength range. Surface optical profile measurements indicate a flatness of the order of 30 nm in the fabricated structures across several millimeters. Single-point spectral measurements on devices show an excellent agreement with simulated optical models, and demonstrate Si-SiOx-Si fixed optical filters with a 94% transmission at 1940 nm with a full-width at half-maximum of 250 nm. Distributed Bragg reflectors demonstrate 90% reflectance across the 1560–2050-nm wavelength range, making them suitable as broadband reflectors. The optical spatial uniformity across a 3-mm $\times 3$ -mm device shows only a 3% variation across the entire optically active area. Finally, the mechanical resonance characteristic of a 1-mm $\times 1$ -mm fabricated device shows the lowest resonant frequency of the suspended structure to be 39 kHz, indicating excellent immunity to extraneous low-frequency vibrations. [2014-0278] [ABSTRACT FROM AUTHOR]

This letter presents the design, fabrication, and optical characterization of silicon-air-silicon-based surface micro-machined distributed Bragg reflectors (DBRs) for the visible to near infrared wavelength range (540–960 nm). The DBR (mirror) consisted of two quarter wave thick silicon films separated by a quarter-wave air gap. A mirror array was successfully fabricated, consisting of mirrors ranging in diameter between 270 and 420 \mu \textm . Calibrated optical measurements indicate that a peak reflectivity close to 92% has been achieved for visible wavelengths, despite the fact that silicon has strong absorbtion in the visible wavelength range. The mirrors are shown to be broadband reflectors, having 85% or more reflectivity over a 160-nm wavelength range. A spatially resolved optical transmission mapping and optical transmission profile of the mirrors demonstrates high uniformity across the fabricated array of DBRs. [2015-0140] [ABSTRACT FROM PUBLISHER]

Examines lattice relaxation of germanium (Ge) islands on silicon (111) measured by scanning tunneling microscopy (STM). Increase in the level of relaxation in Ge islands; Observation of lattice spacing on several islands below the GE lattice constant; Effects of height-to-width aspect ratio on elastic relaxation.

We have performed an extensive first-principles study of the energetics of boron clustering in silicon in the presence of excess self-interstitial atoms (SIAs). We consider complexes with up to four B atoms and two SIAs. We have conducted an extensive search for the ground-state configurations and charge states of these clusters. We find the cluster containing three B atoms and one SIA(B[sub 3]I) to be remarkably stable, while all our clusters with more than 80% boron content are unstable. Hence, we propose B[sub 3]I to be a stable nucleus that can grow to larger clusters. The energetics presented here can be used as input to large-scale predictive models for B diffusion and activation during ion implantation and thermal annealing. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]