Sealed Vacuum Cavity Research Articles

Effect of particle size on the suction mechanism in granular grippers

Granular grippers are highly adaptable end-effectors that exploit the reversible jamming transition of granular materials to hold and manipulate objects. Their holding force comes from the combination of three mechanisms: frictional forces, geometrical constraints, and suction effects. In this work, we experimentally study the effect of particle size on the suction mechanism. Through X-ray computed tomography, we show that small particles (average diameter d approx {120},upmu hbox {m}) achieve higher conformation around the object than larger particles (d approx {4},hbox {mm}), thus allowing the formation of air-tight seals. When the gripper is pulled off, mimicking lifting of an object, vacuum pressure is generated in the sealed cavity at the interface gripper–object. If the particles used as filling material are too large, the gripper does not conform closely around the object, leaving gaps between the gripper’s membrane and the object. These gaps prevent the formation of sealed vacuum cavities between the object and the gripper and in turn hinder the suction mechanism from operating.Graphical abstract

Vacuum Packaging for High-Performance Low Cost MEMS Gyro Used in 6 Degree of Freedom Inertial Navigation System (DOF INS)

Sensors in Motion Inc. is developing a navigation grade 6 DOF MEMS INS using its proprietary and patented technologies. The military is investing in INS and IMU technology which can answer its needs as well as provide the baseline for hundreds of other DOD and commercial applications which need a C-swap sensitive utility. SIM’s technology for MEMS gyros was conceived to address past problems associated with MEMS gyroscopes while leveraging the C-swap benefits of high volume, high yield batch fabrication, automated packaging, self-calibration, and thermal compensation. A key requirement for the MEMS Gyroscope is controlled vacuum-levels to obtain high Q devices. Gyro die are packaged using a multilayer package and getter system, which provides and maintains sealed vacuum cavities. Die are assembled into the LCC package using conventional assembly techniques and the package cavity is sealed using an SST 3150 high-vacuum sealing system. The SST system is used to activate a thin-film getter layer on the package lid before reflow of the solder seal. Resulting pressure levels have been determined by characterizing packaged but unlidded sensor die in a vacuum chamber. The package material, process flow and test results are summarized and reviewed. Tooling, process parameters, and test techniques are explained.

New approach of fabrication and dispensing of micromachined cesium vapor cell

We describe the fabrication of wafer-scale alkali vapor cells based on silicon micromachining and anodic bonding. The principle of the proposed micromachined alkali cell is based on an extremely compact sealed vacuum cavity of a few cubic millimeters containing caesium vapors, illuminated by a high-frequency modulated laser beam. The alkali cells are formed by sealing an etched silicon wafer between two glass wafers. The technique of cell filling involves the use of an alkali dispenser. The activation of cesium vapors is made by local heating of the dispenser below temperature range causing degradations of cesium vapor purity. Thus, the procedure avoids negative effects of cesium chemistry on the quality of cell surfaces and sealing procedure. To demonstrate the clock operation, cesium absorption as well as coherent population trapping resonance was measured in the cells.

Fabrication of capacitive absolute pressure sensor using Si-Au eutectic bonding in SOI wafer

A capacitive absolute pressure sensor was fabricated using a large deflected diaphragm with a sealed vacuum cavity formed by removing handling silicon wafer and oxide layers from a SOI wafer after eutectic bonding of a silicon wafer to the SOI wafer. The deflected displacements of the diaphragm formed by the vacuum cavity in the fabricated sensor were similar to simulation results. Initial capacitance values were about 2.18pF and 3.65pF under normal atmosphere, where the thicknesses of the diaphragm used to fabricate the vacuum cavity were 20 µm and 30 µm, respectively. Also, it was confirmed that the differences of capacitance value from 1000hPa to 5hPa were about 2.57pF and 5.35pF, respectively.

High-accuracy absolute measurement of the refractive index of air

A high-accuracy absolute measurement system of the refractive index of air is proposed. The measurement of the instantaneous index of refraction is achieved by comparing two laser optical paths with a differential laser interferometer. The vacuum optical path length is varied via a motor-driven trapezoidal vacuum cavity moving through a known distance. Compared to other measurement methods, the sealed vacuum cavity requires no vacuum pumping between measurements, and allows this method to function well in industrial applications. The measurement accuracy is better than 5×10–8.

Polysilicon sealed vacuum cavities for microelectromechanical systems

Sealed vacuum cavities are highly useful in silicon-based microelectromechanical systems. Sealed polysilicon cavities serve as reference chambers for commercially available pressure sensors and provide enclosures for high-Q mechanical resonators. They also provide isolation of resonant strain gauges from ambient gases and liquids for use in precision pressure transmitters. The residual pressure in such cavities is less than 10−5 Torr, as evidenced by the polysilicon resonator Q values which can be as high as 300 000. Measured values of Q can be dominated by parasitic electrical resistance losses in the electrical drive circuit. After these losses are accounted for, the dominant loss is due to mechanical radiation of acoustic waves from the supports to the rest of the die and package. The vibration of the beams can be excited and sensed in several different ways for testing purposes. Fiberoptically driven and sensed microbeams operating at up to 510 °C for several hours resulted in no loss of vacuum as evidenced by the restoration of resonator Q upon its return to room temperature. Thus optically resonant microbeams are potentially suitable for fiberoptic-based sensors that withstand harsh environments, including high temperature.

High-sensitivity silicon capacitive sensors for measuring medium-vacuum gas pressures

The design, construction, and preliminary testing of an experimental capacitive silicon pressure sensor are described. The prototype sensor is designed as a robust, precision barometer suitable for measurements on the planet Mars where the mean atmospheric pressure is ~ 6 mbar (600 Pa). Most commercially available silicon pressure sensors tend to operate over pressure ranges ≥ 1 bar, or measure gauge pressure, but this sensor is specifically constructed to measure absolute pressure of 0–10 mbar with a very high sensitivity ~ 1 pF mbar −1. The transductional mechanism is the deflection of a silicon diaphragm under applied pressure across a sealed vacuum cavity. Under storage conditions of 1 bar, the diaphragm displacement is mechanically constrained by an underlying stopping surface. Finite-element analysis shows that typical structures are extremely resistant to overpressure: fracture occurs at many tens of bar. The device is fabricated using a silicon fusion-bonded vacuum cavity which provides for relative insensitivity to temperature changes.

New FET accelerometer based on surface micromachining

A new accelerometer based on an FET sensing element and surface-micromachining technology has been designed and fabrieted. A new process to avoid sticking during processing has been developed. In this new process, the sacrificical layer is etched before polysilicon structuring, defining a sealed vacuum cavity. Finally the accelerometer structure is defined with dry etching on this cavity, avoiding any wet etching process and, in consequences, the sticking of the polysilicon structure on the substrate. The sensing element of the accelerometer is a transistor FET. So the mass of the accelerometer acts as a gate of the transistro, changing the value of the threshold voltage, V T, with the acceleration. Preliminary results show a high sensitivity with a much simpler readout compared to capacitive sensors.