Single-crystal silicon is being increasingly employed in a variety of new commercial products not because of its well-established electronic properties, but rather because of its excellent mechanical properties. In addition, recent trends in the engineering literature indicate a growing interest in the use of silicon as a mechanical material with the ultimate goal of developing a broad range of inexpensive, batch-fabricated, high-performance sensors and transducers which are easily interfaced with the rapidly proliferating microprocessor. This review describes the advantages of employing silicon as a mechanical material, the relevant mechanical characteristics of silicon, and the processing techniques which are specific to micromechanical structures. Finally, the potentials of this new technology are illustrated by numerous detailed examples from the literature. It is clear that silicon will continue to be aggressively exploited in a wide variety of mechanical applications complementary to its traditional role as an electronic material. Furthermore, these multidisciplinary uses of silicon will significantly alter the way we think about all types of miniature mechanical devices and components.

Silicon as a mechanical material

Transparent conductors—A status review

Nanosphere lithography (NSL) is an inexpensive, simple to implement, inherently parallel, high throughput, materials general nanofabrication technique capable of producing an unexpectedly large variety of nanoparticle structures and well-ordered 2D nanoparticle arrays. This article describes our recent efforts to broaden the scope of NSL to include strategies for the fabrication of several new nanoparticle structural motifs and their characterization by atomic force microscopy. NSL has also been demonstrated to be well-suited to the synthesis of size-tunable noble metal nanoparticles in the 20−1000 nm range. This characteristic of NSL has been especially valuable for investigating the fascinating richness of behavior manifested in size-dependent nanoparticle optics. The use of localized surface plasmon resonance (LSPR) spectroscopy to probe the size-tunable optical properties of Ag nanoparticles and their sensitivity to the local, external dielectric environment (viz., the nanoenvironment) is discussed in...

Nanosphere Lithography: A Versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics

Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

We have studied the statistical properties of random surface roughness at the Si-${\mathrm{SiO}}_{2}$ interface using high-resolution transmission electron microscopy (HRTEM). The spectral properties of the HRTEM roughness on normally prepared and intentionally roughened samples appears to be well characterized as a first-order autoregressive or Markovian process which corresponds to an exponential decay in the autocovariance function rather than the usual Gaussian approximation which has been widely used. Such an exponential decay is characterized by tails in the spectrum which are directly attributable to the discrete or steplike nature of the interface roughness which is restricted to occur on crystalline atomic sites. Using a simplified model, we have estimated the effect of projecting the two-dimensional interface roughness through the cross-section thickness to form the one-dimensional boundary studied here. For an isotropic medium, we find that the statistical character of the roughness is preserved during this transformation, but that the rms fluctuation of the roughness is attenuated so that the actual interface is rougher than indicated by the HRTEM technique. After correcting for such averaging, the parameters estimated from the HRTEM are more in agreement with the same parameters used to fit the surface-roughness-limited Hall mobility in metal-oxide-semiconductor field-effect transistor devices.

Surface roughness at the Si(100)-SiO 2 interface

The C KLL spectra from natural diamond, graphite, and single‐crystal β‐SiC have been investigated using x‐ray photoelectron spectroscopy and first‐derivative x‐ray excited Auger electron spectroscopy (XAES). It is shown that the XAES spectra is essentially the same as that obtained with conventional AES with the added benefits of no electron beam (e‐beam) damage, enhanced fine structure, and the simultaneous acquisition of the C 1s and valence‐band spectra. The C KLL XAES fine structure provides a fingerprint of the carbon bonding state and the C 1s and valence‐band spectra provide insight into the origin of this fine structure. Diamondlike carbon films fabricated by hydrogen gas reactive sputtering of graphite on Si were also investigated. The XAES C KLL spectra in conjunction with the valence‐band spectra verifies the tetrahedral C–C bonding in these films even though the AES spectra shows a graphitelike structure; indicative of e‐beam damage.

The C KLL first‐derivative x‐ray photoelectron spectroscopy spectra as a fingerprint of the carbon state and the characterization of diamondlike carbon films

Comparison of the CKLL first-derivative auger spectra from XPS and AES using diamond, graphite, SiC and diamond-like-carbon films

We have reported on the theory of semiconductor‐insulator‐semiconductor (SIS) solar cells in a previous publication. In this paper, the fabrication and properties of indium tin oxide/p‐Si single‐crystal solar cells will be described. The ITO is deposited by the ion‐beam sputtering method. Best photovoltaic devices are obtained when the composition of indium tin oxide (ITO) is 91 mole% and 9 mole% SnO2. The device properties as a function of the ITO composition will be described. The thickness and the composition of the oxide‐silicon interface is critical for device performance. The existence of a thin interfacial layer is demonstrated by Auger spectroscopy. The effect of temperature on device performance and the spectral response are compared with the theory. The SIS model accurately matches the major trends observed in experimental nITO/p‐Si solar cells.

Carl W. Wilmsen

Papers

Surface roughness at the Si(100)-SiO 2 interface

The C KLL first‐derivative x‐ray photoelectron spectroscopy spectra as a fingerprint of the carbon state and the characterization of diamondlike carbon films

Comparison of the CKLL first-derivative auger spectra from XPS and AES using diamond, graphite, SiC and diamond-like-carbon films

The operation of the semiconductor‐insulator‐semiconductor solar cell: Experiment

Oxide layers on III V compound semiconductors