ALBERT

Notizen: Micromachines, including micro scanning tunneling microscope and high force ((approximate)0.1 mN and higher) actuators, are examples of a new class of silicon-based microinstruments for atomic scale surface imaging and modification, as well as submicrometer scale material investigations. A large class of such microinstruments and sensors consist of actuators, such as interdigitated comb drives, that generate force, F, in the form F=βV2, where β is a constant and V is the applied voltage. Such actuators often move a large distance during actuation so that the restoring force, R, of the springs varies nonlinearly with x, i.e., the springs behave as hard springs, and R=K1x+K3x3+... (restoring force is similar for +ve and −ve x due to symmetry). β and Ki, i=1,3,..., of the micro-actuators usually differ from their design values due to processing nonuniformities. Hence, evaluation of these constants becomes necessary for each actuator, and is essential for the instruments that are employed to study materials' behavior on a small scale. In this article, a methodology is developed to calibrate microinstruments, i.e., to evaluate the values of β and Ki, i=1,3,... . The method is based on buckling of a long slender beam of known dimensions, and made of a material with known property (elastic modulus). Buckling is achieved by an axial compressive force on the beam applied by the actuator of the microinstrument. β and Ki are derived from the relation between the applied voltage on the actuator, and the post buckling deformation of the beam. The beam is designed and cofabricated with the actuator, and hence the calibration mechanism is integrable with each microinstrument. An analysis is provided to estimate the possible errors in calibration due to errors in the measured dimensions of the calibrating beam. It is shown that the calibration error increases linearly with the error in the measured linear dimensions. The applicability of the method is demonstrated by fabricating microinstruments, which, prior to their calibration, are employed to apply torque on single crystal silicon bars (in the form of pillars), until the bars fracture. The instruments are then calibrated, and the calibrated values of β and Ki are used to evaluate the torques applied on the bars at different voltages. Stresses to fracture of the bars are also estimated. The torsion experiment is an example of the application of integrated microinstruments for small scale material studies. © 1998 American Institute of Physics.

Notizen: Two versions of micro-scanning tunneling microscopes (micro-STMs) have been fabricated. The integrated micro-STMs are fabricated from single crystal silicon using the high-aspect-ratio SCREAM process. Each micro-STM includes integrated xy comb drive actuators and a torsional z actuator with integrated cantilever and tip. One micro-STM measures approximately 200 μm on-a-side and is an example of a STM element for a STM array architecture. Another, larger micro-STM/atomic force microscope measures 2 mm on-a-side including a 1 mm long cantilever with a 20 nm diam tip. We demonstrate the operation of this larger STM by obtaining a STM image of a 200 nm metal conductor on a silicon chip. © 1995 American Institute of Physics.

Notizen: Room-temperature Hall mobilities exceeding 900 cm2/V s are obtained for AlGaN/GaN heterostructures on (111) Si by single-temperature flow modulation organometallic vapor phase epitaxy. Thin pseudomorphic AlGaN top layers exhibit a 1.5 nm surface roughness and induces a two-dimensional electron gas sheet carrier concentration of 1.0×1013 cm−2. The GaN buffer layer has a background carrier concentration of 1.0×1015 cm−3, 130 arcsec x-ray diffraction full width at half maximum, and a low-temperature photoluminescence linewidth of 10 meV. An AlN nucleation layer provides static electrical isolation between the AlGaN/GaN and the conducting Si substrate. Large crack-free areas of high-crystalline-quality epitaxial material are obtained and have been successfully used for transistor fabrication. © 2000 American Institute of Physics.

Notizen: A surface micromachined suspended interferometer and an atomic force microscope (AFM) are incorporated into a novel optical reading technique. The AFM tip mechanically deflects the suspended membrane as it scans past a data bit on the membrane surface. The data are read by monitoring the changing interference pattern generated in the optical aperture of the interferometer. When operated in parallel, there exists the potential for high speed, high density data reading. © 1996 American Institute of Physics.

Notizen: The selective deposition of compound semiconductors on single crystal silicon tip arrays produces optical quality, direct band gap materials on the silicon nanostructures. We demonstrate using the organometallic vapor phase epitaxy of GaInP that the direct band gap semiconductor nucleates selectively on the silicon tips. The structural properties of the tips (whose radius of curvature is approximately 10–20 nm) are unaltered by this chemical vapor deposition process. Furthermore, intense band edge emission from the GaInP is observed with an external electron beam or laser stimulation indicating a good crystal quality for the three dimensional epitaxial structures. © 1997 American Institute of Physics.

Notizen: Optically aided reading and writing of gold and tungsten mounds on proton-implanted, multiple quantum well InGaAs/GaAs wafers has been demonstrated using an atomic force microscope (AFM). The system is relatively simple, requiring only a diode laser as the light source, providing a novel, compact, optoelectronic memory system. © 1995 American Institute of Physics.