Electrical Feedthroughs Research Articles

Electron-beam tip/sample heating device for a scanning tunneling microscopy

We present an electron-beam heating device for a scanning tunneling microscopy (STM) that can be used for heating both the STM tip and the sample to 2200K. Mounted on a linear bellows with electrical feedthroughs, the device can be readily installed into the transfer path of a vacuum load lock. We demonstrate the heating capability of the device by flash cleaning Ru(0001) and Fe(001) crystals, and W tips. The flash-cleaned W tips are coated with Fe and further used for spin-polarized imaging of the Mn∕Fe(001) system.

CVD diamond thin film technology for MEMS packaging

Due to its extreme hardness, chemical and mechanical stability, large band gap and highest thermal conductivity, poly-crystalline diamond (poly-C) is expected to be an excellent packaging material for biomedical and environmental MEMS devices. A poly-C thin film packaging technology has been developed to explore the application of this novel material on post-MEMS encapsulation packaging process. To study the poly-C thin film packaging a testchip was fabricated using PECVD deposited oxide as a sacrificial material. Large access ports were opened along the package edge to release thin film package using oxide etch. Then, additional poly-C growth was used to seal the access ports. In the test package, boron doped poly-C was also studied as the material for electrical feedthroughs that can be embedded into the undoped electrically insulating poly-C package. This poly-C thin film packaging process and the all-diamond packaging concept has been developed for the first time.

A wireless microsystem for the remote sensing of pressure, temperature, and relative humidity

This work presents a microsystem that utilizes inductive power and data transfer through a backscatter-modulated carrier and a transducer interface that monitors its environment through embedded capacitive transducers. Formed on a single chip, transducers for temperature, pressure, and relative humidity are realized using a silicon-on-glass process that combines anodic bonding and a silicon-gold eutectic to realize vacuum-sealed cavities with low-impedance (6 /spl Omega/) electrical feedthroughs. Temperature is sensed capacitively using a row of Si/Au bimorph beams that produce a sensitivity of 15 fF//spl deg/C from 20 to 100/spl deg/C. The absolute pressure sensors have a sensitivity of 15 fF/torr and a range from 500 to 1200 torr, while the relative humidity sensor responds with 39 fF/%RH from 20 to 95%RH. A relaxation oscillator implements low-power capacitance-to-frequency conversion on a second chip with a sensitivity of 750 Hz/pF at 10 kHz, forming a 341 /spl mu/W transducer interface. The system is remotely powered by a 3-MHz carrier and has a volume of 32 mm/sup 3/, including the hybrid antenna wound around the perimeter of the system.

Localized induction heating solder bonding for wafer level MEMS packaging

This paper reports a new solder bonding method for the wafer level packaging of MEMS devices. Electroplated magnetic film was heated using induction heating causing the solder to reflow. The experiment results show that it took less than 1 min to complete the bonding process. In addition, the MEMS devices experienced a temperature of only 110 °C during bonding, thus thin film materials would not be damaged. Moreover, the bond strength between silicon and silicon wafer was higher than 18 MPa. The step height of the feed-through wire (acting as the electrical feed-through of the bonded region) is sealed by the electroplated film. Thus, the flatness and roughness of the electroplated surface are recovered by the solder reflow, and the package for preventing water leakage can be achieved. The integration of the surface micromachined devices with the proposed packaging techniques was demonstrated.

Atom-chip Bose-Einstein condensation in a portable vacuum cell

A $^{87}\mathrm{Rb}$ Bose-Einstein condensate (BEC) is produced in a portable atom-chip system less than $30\ifmmode\times\else\texttimes\fi{}30\ifmmode\times\else\texttimes\fi{}15\phantom{\rule{0.3em}{0ex}}\mathrm{cm}$, where the ultrahigh vacuum is maintained by a small, $8\phantom{\rule{0.3em}{0ex}}\mathrm{L}∕\mathrm{s}$, ion pump and nonevaporable getter. An aluminum nitride chip with lithographically patterned copper is used to seal the vacuum system, provide the electrical feedthroughs, and create the magnetic trap potentials. All cooling and trapping processes occur $0.6--2.5\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$ from ambient laboratory air. A condensate of about 2000 $^{87}\mathrm{Rb}$ atoms in $F=2,{m}_{F}=2$ is achieved after $4.21\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ of rf forced evaporation. A magneto-optical trap lifetime of $30\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ indicates the vacuum near the chip surface is about ${10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}\text{torr}$. This work suggests that a chip-based BEC-compatible vacuum system can occupy a volume of less than $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{L}$.

A Low-Temperature Thin-Film Electroplated Metal Vacuum Package

This paper presents a packaging technology that employs an electroplated nickel film to vacuum seal a MEMS structure at the wafer level. The package is fabricated in a low-temperature (<250/spl deg/C) 3-mask process by electroplating a 40-/spl mu/m-thick nickel film over an 8-/spl mu/m sacrificial photoresist that is removed prior to package sealing. A large fluidic access port enables an 800/spl times/800 /spl mu/m package to be released in less than three hours. MEMS device release is performed after the formation of the first level package. The maximum fabrication temperature of 250/spl deg/C represents the lowest temperature ever reported for thin film packages (previous low /spl sim/400/spl deg/C). Implementation of electrical feedthroughs in this process requires no planarization. Several mechanisms, based upon localized melting and Pb/Sn solder bumping, for sealing low fluidic resistance feedthroughs have been investigated. This package has been fabricated with an integrated Pirani gauge to further characterize the different sealing technologies. These gauges have been used to establish the hermeticity of the different sealing technologies and have measured a sealing pressure of /spl sim/1.5 torr. Short-term (/spl sim/several weeks) reliability data is also presented.

DLC coating of a few microns in thickness on three-dimensional substrates

Uniform coating of the thick diamond-like carbon (DLC) on three-dimensional substrates was studied using a hybrid process of plasma-based ion implantation and deposition (PBIID). In the PBIID system, an RF pulse for plasma generation and a negative high-voltage pulse for ion implantation were supplied to a substrate through a single electrical feedthrough. Then the high-density plasma was produced along the substrate, leading to the formation of uniform coating film and the ion implantation on three-dimensional substrates. Ion implantation by PBII technique served to the reduction in compressive residual stress of DLC film and the formation of mixing layer between the DLC film and the substrate. As a result, the thick and good-adhesive DLC film with more than a few μm in thickness was almost uniformly prepared on the surface of cylindrical pipe, triangle prism, and trench structure. The deposition rate was approximately 1 μm/h using the toluene as a precursor gas. The hardness of the DLC films was found to be about 12 GPa by nano-indentation method.

Chip-level vacuum packaging of micromachines using nanogetters

A new approach to vacuum packaging of micro-machined resonant, tunneling, and display devices is covered in this paper. A multi-layer, thin-film getter, called a NanoGetter, which is particle free and does not increase the chip size of the microsystem has been developed and integrated into conventional wafer-to-wafer bonding processes. Hermetic electrical feedthroughs are also provided as part of this total-solution technology. Experimental data taken with silicon resonators is presented in which Q values in excess of 21,000 have been obtained. Applications for this technology include gyroscopes, accelerometers, displays, flow sensors, density meters, infrared (IR) sensors, microvacuum tubes, radio frequency microelectromechanical systems (RF-MEMS) and pressure sensors.

Endpoint detectable plating through femtosecond laser drilled glass wafers for electrical interconnections

An endpoint detectable plating process to avoid over-electroplating was proposed and performed in this work. The technology was developed for fabrication of Pyrex glass wafer with electrical feed-throughs. Thin film of gold was deposited on the glass wafer prior to the femtosecond laser drilling. When the growing metal in the through-holes was contacted to the metal, a resistance between the opposite two electrodes decreases suddenly. Thus, the endpoint detection was realized by in situ monitoring of applied voltage at constant current mode. After the endpoint detection, periodic reverse plating was applied to fill the through-holes uniformly. Finally, uniform copper deposition in the through-holes up to 12 aspect ratios was realized by this method. This technology was also applicable to the fabrication of microstructure based on electroforming.

Batch processing of CMOS compatible feedthroughs

This paper presents a technique for batch fabrication of electrical feedthroughs in CMOS wafers. The presented process is designed with specific attention on industrial applicability. The electrical feedthroughs are processed entirely by low temperature, CMOS compatible processes. Hence, the process scheme allows for post processing of feedthroughs in any kind of fully processed CMOS wafer. The fabrication of the electrical feedthroughs is based on wet etching of through-holes, low temperature deposition of dielectric material, and electrodeposition of photoresist and feedthrough metal. The feedthrough technology employs a simple solution to the well-known CMOS compatibility issue of KOH by protecting the CMOS side of the wafer using sputter deposited TiW/Au. The fabricated feedthroughs exhibit excellent electrical performance having a serial resistance of 40 mΩ and a parasitic capacitance of 2.5 pF.

MEMS-Based Solid Propellant Rocket Array Thruster with Electrical Feedthroughs.

The prototype of a solid propellant rocket array thruster for simple attitude control of a 10 kg class micro-spacecraft was completed and tested. The prototype has 10×10 φ0.8 mm solid propellant micro-rockets arrayed at a pitch of 1.2 mm on a 20×22 mm substrate. To realize such a dense array of micro-rockets, each ignition heater is powered from the backside of the thruster through an electrical feedthrough which passes along a propellant cylinder wall. Boron/potassium nitrate propellant (NAB) is used with/without lead rhodanide/potassium chlorate/nitrocellulose ignition aid (RK). Impulse thrust was measured by a pendulum method in air. Ignition required electric power of at least 3–4 W with RK and 4–6 W without RK. Measured impulse thrusts were from 2×10−5 Ns to 3×10−4 Ns after the calculation of compensation for air dumping.

Fabrication of high-density electrical feed-throughs by deep-reactive-ion etching of Pyrex glass

This paper describes the fabrication technology for high-density electrical feed-throughs in Pyrex glass wafers. Small through holes (40-80 /spl mu/m in diameter) in Pyrex glass wafers have been fabricated using deep-reactive-ion etching (DRIE) in a sulfur hexafluoride (SF/sub 6/) plasma. The maximum aspect ratios obtained were between 5 and 7 for a hole pattern and 10 for a trench pattern. Through the wafer etching of a hole pattern of 50 /spl mu/m diameter was carried out using 150-/spl mu/m-thick Pyrex glass wafers. The electrical feed-throughs in the wafers were fabricated by filling the through-holes with electroplated nickel. We were able to successfully bond the glass wafer to silicon by anodic bonding after removing the electroplated nickel on the surface of the wafer by chemical-mechanical polishing (CMP). The electric resistance of the feed-through was estimated by a 4 point wire sensing method to be about 40 m/spl Omega/ per hole. The heat cycles test shows that the resistance changes were within 3% after 100 cycles. The fabrication of high density electrical feed-throughs is one of the key processes in the field of MEMS. Probable applications of this technology are in electrical feed-throughs between logic elements and microprobe arrays for high-density data storage and for packaged devices.

An upgraded brazing technique to manufacture ceramic-metal joints for UHV applications

The properties of an upgraded active vacuum brazing procedure, explicitly developed to manufacture ceramic-metal joints, are presented and some of the most significant applications described. The essential feature of the technique is the use of AgCuTi as brazing material, which permits the joining of alumina (Al 2O 3) very reliably with various metals, including stainless steel. The careful control of the brazing cycle and the quality of the alumina, in terms of purity and density, play an essential role in determining the final performances of the components. With the technology presented, several vacuum components have been developed and manufactured, among which the most interesting are electrical feedthroughs compatible with commercially available signal connectors and capable of operating at temperatures of 500°C or higher. In particular, a completely new model of a signal feedthrough, to be used with the Minisnap-Plug of Odu and presenting an alumina–stainless steel joint, has been developed and thoroughly tested in the laboratory. Its performances have been verified at more than 700°C, with temperature variations of up to 10°/min. The latest version of these feedthroughs has shown good vacuum tightness and reliability up to 650°C and therefore presents better characteristics than most of the feedthroughs commercially available. In addition to being tested on the bench, some feedthroughs have been used in the nuclear fusion experiment Reversed Field eXperiment (RFX), without showing any sign of degradation or ageing.

Application of ion imaging to the electron impact ionization of oxygen using crossed beams and a custom designed fast multichannel pulse generator

In this article we introduce the application of ion imaging to the detection of product ions produced in electron–molecule collisions. Unlike photoinitiation experiments in which a short duration laser pulse is used to excite a reagent molecule or to prepare an exotic species for subsequent reaction, collisions involving electrons (or ions) involve field-sensitive charged beam pulses of longer duration than laser pulses. Such experiments require the fast switching of electric fields with particular attention to the elimination of stray fields, contact potentials, and noise pickup on cables and electrical feedthroughs. We have recorded preliminary O2+ and O+ ion images from 100 eV electron impact ionization of O2 supersonic molecular beams. The triggering of the nozzle, field plates, electron gun, and repeller/extractor elements was achieved using a low cost, versatile, fast multichannel pulse generator with fiber-optic coupling that was designed to produce low noise trigger pulses for commercial and custom made pulsed high voltage power supplies.

High pressure hydrogen loading cell for photoconductivity measurements down to the milliKelvin regime

A gas loading cell has been developed to load rare earth thin film samples with hydrogen at pressures up to 200 bars at room temperature. A miniature valve closes the gas inlet, after which the cell is suspended from the cold tail of a He3 flow cryostat into the bore of a 16 T superconducting magnet. An ultraviolet stroboscope outside the cryostat illuminates the sample by way of an optical fiber to a window in the cell. Electrical feedthroughs permit photoconductivity and magnetotransport measurements over three decades in temperature. Extension to other materials, different gas atmospheres, and helium dilution refrigerator temperatures is straightforward.

Development of a High Lateral Resolution Electron Beam Induced Current Technique for Electrical Characterization of InGaN-Based Quantum Well Light Emitting Diodes

ABSTRACTElectron Beam Induced Current (EBIC) is a Scanning Electron Microscope (SEM)-based technique that can provide information on the electrical properties of semiconductor materials and devices. This work focuses on the design and implemenation of an EBIC system in a dedicated Scanning Transmission Electron Microscope (STEM). The STEM-EBIC technique was used in the characterization of an Indium Gallium Nitride (InGaN) quantum well Light Emitting Diode (LED). The conventional “H-bar” Transmission Electron Microscopy (TEM) sample preparation method using Focused Ion Beam Micromachining (FIBM) was adapted to create an electron-transparent membrane approximately 300 nm thick on the sample while preserving the electrical activity of the device. A STEM-EBIC sample holder with two insulated electrical feedthroughs making contact to the thinned LED was designed and custom made for these experiments. The simultaneous collection of Z-contrast images, EBIC images, and In and Al elemental images allowed for the determination of the p-n junction location, AlGaN and GaN barrier layers, and the thin InGaN quantum well layer within the device. The relative position of the p-n junction with respect to the thin InGaN quantum well was found to be (19 ± 3) nm from the center of the InGaN quantum well.

Development and characterisation of a visible light photon counting imaging detector system

We report on the development of a visible light photon counting imaging detector system. The detector concept is based on standard 25 mm diameter microchannel plate image intensifiers made by Proxitronic in Bensheim (Germany). Modifications applied to these image intensifiers are the use of three microchannel plates instead of two and a high resistance ceramics plate used instead of the standard phosphor output screen. A wedge and strip anode mounted directly behind the high resistance ceramics plate was used as a read out device. This wedge and strip anode picks up the image charge of electron clouds emerging from the microchannel plates. The charge pulses are fed into four charge amplifiers and subsequently into a digital position decoding electronics, achieving a position resolution of up to 1024×1024 pixels . Mounting the anode outside the detector tube is a new approach and has the great advantage of avoiding electrical feedthroughs from the anode so that the standard image intensifier fabrication process can be applied to produce these photon counting detector tubes. First results of the characterization of gain, homogeneity, dark current and imaging linearity are presented.

Position sensitive anodes for MCP read-out using induced charge measurement

We investigate the method of an indirect detection of a MCP charge avalanche projected onto a resistive layer (G. Battistoni, et al., Nucl. Instr. and Meth., 202 (1982) 459). If the sheet resistance is favourable one can detect the charge cloud by the capacitive coupling to an anode structure a few millimetres behind the layer. The anode structure can be, for example, a wedge-and-strip electrode pattern (M. Unverzagt, Diplomarbeit, Universität Frankfurt 1992, private communication) as it is used for directly collecting the electron avalanche from a MCP. Detection of the induced charge is beneficial in several respects. Firstly, image distortions produced by secondary electron mediated charge redistribution are eliminated. Secondly, the noise component due to quantized charge collection, commonly referred to as partition noise, is not present. In addition, the dielectric substrate can function both as an element of the vacuum enclosure and HV insulator, making the electrical connections easily accessible and the pattern operable at ground potential, independently of detector operating voltages. This technique can be used to simplify the electronic design requirements where varying high voltages are required at the detector input face such as plasma analysers, etc. It also has application in the manufacture of intensifier tubes (J. Barnstedt, M. Grewing, Nucl. Instr. and Meth., these proceedings) where the inclusion of a readout pattern inside the intensifier body with associated electrical feed-throughs can prove problematic. We will present data on the performance of such detection geometries using several types of charge division anode, and discuss the advantages compared with the “traditional” charge collecting method.

The influence of solder fillet geometry on the occurrence of corona discharge during operation between 400 and 900 V in partial vacuum

A number of experiments have been made to study the effect that different solder joint designs have on the voltage needed to initiate the onset of corona discharge under low ambient pressures. Wires were joined to both printed circuit board terminations and to electrical feedthroughs. All were constructed from materials known to be suitable for spacecraft. The main factor that determines whether solder joints will be prone to initiate corona discharges or electrical breakdown in a space environment is the actual minimum distance between terminals. Large, rounded solder fillets are desirable, but those containing protrusions or contours around wire strands have little adverse effect. It is shown that it is not always necessary, as is usually required by workmanship specifications related to high voltage connections, for operators to rework solder joints in order to achieve protrusion-free fillets. It would appear from metallurgical analyses of solder joints that it is the tin-rich phase that is sputtered from the fillet's surface during the phenomenon of corona discharge.

A low-pressure encapsulated resonant fluid density sensor with feedback control electronics

In this paper we present a fully low-pressure encapsulated and closed-loop operated resonant fluid density sensor. The device consists of a tube in silicon, which is vibrating in a selected balanced torsion mode. The resonance frequency changes with the density of the fluid in the tube due to the change of the inertial mass of the vibrating system. The sensor is fabricated and encapsulated at wafer level using silicon micromachining techniques. The encapsulation is performed by anodically bonding the silicon densitometer in vacuum between two glass lids with metal electrodes for electrostatic excitation and capacitive detection. The sample volume is only 0.035 ml and the size of the encapsulated device is 14 mm × 23 mm × 1.85 mm. The measurements were performed using a novel excitation and detection technique based on discontinuous, `burst' excitation. This principle enabled us to eliminate the electrical crosstalk between excitation and detection. The electrodes could be placed on top of the glass lids without using electrical feedthroughs, and a cavity gap of 100 µm could be formed between the recessed glass lid surface and the silicon tube to reduce squeeze-film damping. The closed-loop `burst' technology enabled us to make continuous measurements of fluid densities. The sensor showed high density sensitivities of the order of -200 ppm (kg m-3)-1, a high mechanical Q-factor of 3400 for air in the tube and low temperature sensitivities of -29 ppm °C-1 in the range 20-100 °C.