X-Ray Diffraction Method to Detect Defects in Cubic Semiconductor (100) Wafers
This technology is a method of using x-ray diffraction (XRD) to evaluate the concentration of crystal structure defects, and thus the quality, of cubic (100)-oriented semiconductor wafers. Developed to enhance NASA's capabilities in fabricating chips for aeronautics applications, the method supplants existing methods that not only destroy the wafer in question, but can take as long as a day to determine the quality of a single wafer. The approach can be used with any commonly used semiconductor, including silicon, SiGe, GaAs and others, in a cubic (100) orientation, which covers at least 90% of commercial wafers. It can also be used to evaluate the quality of epi layers deposited on wafer substrates, and of ingots before they are sliced into wafers.
electrical and electronics
Double Sided Si(Ge)/Sapphire/III-Nitride Hybrid Structures
III-nitride devices are commonly made on sapphire substrates today for various commercial electronic and optoelectronic applications. Thus, this innovation relates directly to the combination of devices on opposite sides of the sapphire substrate. One possible device combination is to have LEDs one side and solar cells on the other, such as for displays.
electrical and electronics
High Mobility Transport Layer Structures for Rhombohedral Si/Ge/SiGe Devices
Performance of solar cells and other electronic devices such as transistors can be improved greatly if carrier mobility is increased. Si and Ge have Type-II bandgap alignment in cubically strained and relaxed layers. Quantum well and super lattice with Si, Ge, and SiGe have been good noble structures to build high electron mobility layer and high hole mobility layers. However, the atomic lattice constant of Ge is bigger than that of Si and direct epitaxial growth generates large density of misfit dislocations which decrease carrier mobility and shorten device life time. So it required special buffer layers such as super lattice or gradient indexed layers to grow Ge on Si wafers or Si on Ge wafers. The growth of these buffer layers takes extra effort and time such as post-annealing process to remove dislocations by dislocation gliding inside buffer layer. This invention is a fabrication method for high mobility layer structures of rhombohedrally aligned SiGe on a trigonal substrate. The invention utilizes C-plane (0001) Sapphire which has a triangle plane, and a Si (Ge) (C) (111) crystal or an alloy of group TV semiconductor (111) crystal grown on the Sapphire.
Compact Sensor for In-Situ Gas Species Determination and Measurement
NASA's gas sensor was originally developed for the storage of volatile liquids and high-pressure gases in outer space in order to facilitate space travel. The innovation has a diverse array of applications beyond aerospace, including cryogenic environments, pressurized or vacuum conditions, and hazardous locations. The sensor system is composed of 1) a fiber-coupled laser light source, 2) a fiber-coupled photodiode detector, and 3) an optical interferometer. The non-intrusive sensor employs a number of optical techniques to measure gas density, temperature, type of species present, and concentration of various species. When the sensor is placed in the area where a gas leak may be present, gas density is detected and recorded as a result of changes in light transmission through the fiber. Changes in the density of gas in the test region cause corresponding changes in the intensity output onto a photodiode detector. This process provides a real-time, temporal history of a leak. Gas temperature is determined by placing an optical fiber along the length of a structure for in-situ measurements. The type of gas species present can be determined by using optical line emission spectrometry. The light-based sensor uses these interferometric and spectroscopic techniques to obtain real-time, in-situ measurements that have been successfully tested in environments with a pressure range of 20 mtorr to 760 mtorr. Commercially available gas detection methods are limited in several ways. Vacuum gauges can detect only certain gases, and they have a limited operational range. Mass spectrometer systems are able to perform well, but their size, bulk, and use of high voltage, which can potentially cause arcing and ignition of combustible propellants, severely limit their usefulness. NASA's compact gas detection sensor has numerous advantages over other state-of-the-art detection techniques. Because the sensor is rugged, compact, and lightweight, it can be used in small, remote areas where other devices will not fit. It has no electronic ignition device, making the system suitable for use in explosive or hazardous environments. The system measures gas density, temperature, type, and concentration in real time, providing critical information on both the severity and location of the leak, all while consuming minimal power at very low cost.
Process for fabricating superconducting circuitry on both sides of an ultra-thin silicon (Si) layer.
This fabrication method allows for a minimalistic silicon wafer to be used as a circuit board while reducing space and increasing efficiency by depositing superconducting material on both sides. Due to the thin nature of the silicon wafer, an additional backing handle wafer is required during the fabrication of this circuitry to allow for deposition of metal thin film on a hot substrate on one side of the wafer. In addition, a metallic and polymeric sacrificial layer is used to protect the silicon substrate and superconducting metallic layers during removal of the unwanted silicon, buried oxide, and epoxy layers. This process introduces the fabrication methodology required to realize the ultra-low loss transmission lines and ultra-low crosstalk between superconducting sensors.
Diamond Pellet Grinding Tool
The NASA Marshall invention makes use of a template fabricated via 3D printing that encapsulates diamond pellets and fits over a CNC tool head. The unique design solves the problems associated with similar, commercially available designs where other types of fixtures articulated, or gave way, too much, rendering those previous tools ineffective. By encapsulating the diamond pellets in a 3D printed template whose stiffness and articulation can be controlled by air pressure and thickness, mid-spatial frequency errors are eliminated at their source. The tool was originally developed to address recurring issues in fabricating UV and x-ray optical surfaces, but can be used for visible-range optical surfaces or for any surface that requires precision finishing, whether curved, flat or aspheric. This could include medical devices like artificial joints, as well as semiconductor wafers, sapphire windows and many others. By reducing the processing time in polishing complex surfaces by as much as half, the NASA invention can also reduce costs. Using the NASA tool, very low arc-second resolution mirrors can be fabricated on a robotic polisher. The tool can be set up and used in less than one day and can be rebuilt quickly, with few components requiring replacement. The tool can be used on glasses, metals and other materials used for optics and precision surfaces.
electrical and electronics
Nanostructure-Based Vacuum Channel Transistor
A planar lateral air transistor was fabricated using standard silicon semiconductor processing. The emitter and collector were sub-lithographically separated by photoresist ashing, with the curvature of the tip controlled by the thermal reflow of the photoresist. The gap can be shrunk as small as 10nm using this process. Since the nanogap separating the emitter and collector is smaller than the electron mean free path in air, vacuum is not needed. The present structure exhibits superior gate controllability and negligible gate leakage current due to adoption of the gate insulator. The device has potential for high performance and low power applications; also, since vacuum as the carrier transport medium is immune to high temperature and radiation, the proposed nanotransistors are ideal for extreme environments. Process and layout refinements such as coating a low work function material on the emitter, reducing the overlap area and optimizing the oxide thickness can potentially improve the cut-off frequency well into the THz regime.
materials and coatings
High Precision Metal Thin Film Liftoff Technique
The purpose of this innovation is to pattern thin metal films on a silicon substrates. These thin metal films can be deposited using physical vapor deposition techniques, which include thermal evaporation, electron-beam evaporation, and DC magnetron sputtering. The steps involved to realize this innovation include fabricating the liftoff mask, depositing the metal, and lifting off the metal in acetone. Fabrication of the liftoff mask consists of spinning on the polymer layer, depositing the germanium layer, patterning the germanium layer using a polymeric photoresist, etching the germanium layer using a reactive ion etcher (RIE), and etching the polymer layer using an oxygen plasma. Alternate embodiments of this innovation involve using different polymer layer materials and different germanium thicknesses. This innovation requires the use of standard photolithographic equipment, which includes a spin coater, a hotplate, and a mask aligner. It also requires the use of a reactive ion etcher (RIE) to etch the germanium and ash the polymer layers. The novel features of this innovation are the high degree of control over the thicknesses of each liftoff mask layer and the amount of undercut in the polymer layer. The undercut is precisely and reproducibly controlled inside the RIE by setting the amount of oxygen gas flow, power, and ash time.
robotics automation and control
Digital Machine Control Electronics
The SCAPS (Single-Coil Absolute Position Sensor) GAPSYN (Inductive Gap Sensor) Digital Signal Conditioning Electronics technology (MFS-32318-1) provides voltage that is proportional to the position of the sensor. This circuit processes two signals from the position sensor to determine the amplitude of an amplitude-modulated signal from the position sensor, correcting for gap fluctuations and nonlinearities. An Absolute Limit Switch (MFS-32192-1) utilizes the SCAPS technology to produce an absolute limit switch point, such as to stop a movable carriage. The system for sensing the position of a rotor in a hybrid stepper motor (MFS-32402-1) is a rate-insensitive (i.e., operates at any speed, including zero rate), linear feedback sensor system that can be used for controlling two-phase and multi-phase stepper motors. The Micro-Commanding Servo Motor Controller With Greater Than Fifty Million To One Dynamic Rate Range technology (MFS-31529-1) senses rotary position of a drive shaft to derive appropriate drive signals for a motor. The Short-Range Antenna/Close-Proximity Transmitter and Receiver technology (MFS- 32228-1) is an inexpensive and effective method of exchanging information over a short distance between two devices when each is equipped with a SCAPS coil.
Multispectral Imaging, Detection, and Active Reflectance (MiDAR)
The MiDAR transmitter emits coded narrowband structured illumination to generate high-frame-rate multispectral video, perform real-time radiometric calibration, and provide a high-bandwidth simplex optical data-link under a range of ambient irradiance conditions, including darkness. A theoretical framework, based on unique color band signatures, is developed for multispectral video reconstruction and optical communications algorithms used on MiDAR transmitters and receivers. Experimental tests demonstrate a 7-channel MiDAR prototype consisting of an active array of multispectral high-intensity light-emitting diodes (MiDAR transmitter) coupled with a state-of-the-art, high-frame-rate NIR computational imager, the NASA FluidCam NIR, which functions as a MiDAR receiver. A 32-channel instrument is currently in development. Preliminary results confirm efficient, radiometrically-calibrated, high signal-to-noise ratio (SNR) active multispectral imaging in 7 channels from 405-940 nm at 2048x2048 pixels and 30 Hz. These results demonstrate a cost-effective and adaptive sensing modality, with the ability to change color bands and relative intensities in real-time, in response to changing science requirements or dynamic scenes. Potential applications of MiDAR include high-resolution nocturnal and diurnal multispectral imaging from air, space and underwater environments as well as long- distance optical communication, bidirectional reflectance distribution function characterization, mineral identification, atmospheric correction, UV/fluorescent imaging, 3D reconstruction using Structure from Motion (SfM), and underwater imaging using Fluid Lensing. Multipurpose sensors, such as MiDAR, which fuse active sensing and communications capabilities, may be particularly well-suited for mass-limited robotic exploration of Earth and the solar system and represent a possible new generation of instruments for active optical remote sensing.