Buried Electrodes Research Articles

3-D self-assembling and actuation of electrostatic microstructures

An advanced three-dimensional (3-D) self-assembling technique of surface micro-machined polysilicon structures is presented here for the realization of dedicated actuators for optical applications such as micro-mirror arrays with large deflection angles. Three-dimensional polysilicon microparts are self-assembled by beam buckling induced by integrated scratch drive actuators (SDAs). With this technique, 380/spl times/250 /spl mu/m/sup 2/ microplates were lifted 30 /spl mu/m above the substrate plane. Once the assembling is performed, the 3-D shapes were held permanently by an integrated mechanical lock. Subsequent to the 3-D assembling, micro-mirrors were successfully actuated by biasing buried electrodes. Controlled motion up to /spl plusmn/15/spl deg/ rotation was measured and analyzed by means of analytical models. Long-term actuations were carried out without any observable change, even for 0.5-/spl mu/m thin polysilicon structures. This self-assembling technique of 3-D devices from surface micro-machining opens new integration capabilities and new applications for micro-opto-electro-mechanical systems (MOEMS).

Micromechanical voltage reference using the pull-in of a beam

The pull-in voltage of a single-side anchored freestanding beam, under lateral deflection, has been investigated for application as a DC voltage reference. Two sets of electrodes, along side the tip, are used for parallel-plate type of electrostatic actuation of the 200 /spl mu/m long beam in the plane of the wafer. Another set of buried electrodes is aligned with the plate electrode at the free-standing tip and is used as a differential capacitor for the simultaneous detection of the displacement, with the purpose to determine the stability border and thus the pull-in voltage. The single-end clamping ensures that the pull-in voltage is insensitive to technology-induced stresses. A 2D energy-based analytical model for the static pull-in is compared with measurements. Bifurcation diagrams are computed numerically, based on a local continuation method. Devices have been designed and fabricated in an epi-poly process. Measurements are in agreement with modeling and confirm a pull-in voltage in the 9.1-9.5 V range. Reproducibility is limited by hysteresis and charging of the dielectric layer in between the electrodes. The device can be operated in feedback or as a seesaw, by using the two sets of electrodes.

Electrical double‐dipole experiment in the German Continental Deep Drilling Program (KTB)

Among the most important rationales to drill the German Continental Deep Drilling Program (KTB) borehole was the necessity to calibrate geophysical methods. Deep and hitherto inaccessible seismic reflectors, high‐conductivity layers, and temperature belong to this group of deep crustal properties which can be predicted from surface measurements, but whose depth and nature are a matter of dispute. One problem is the unknown influence of inhomogeneous superficial layers on the determination and resolution of the model parameters. In the case of electrical resistivity a number of presite experiments had detected a high‐conductivity layer of regional extent at a mean depth of ∼10 km. Distorting superficial layers were expected to cause severe ambiguity in the interpretation of the specific properties of this layer, even feigning its existence at all. The drilling yielded direct evidence of high‐conductivity material within the range of 8 km depth. After completion of the KTB a large‐scale dipole‐dipole experiment was carried out using a vertical electric receiver dipole with one of the electrodes in the main drill hole at 9065 m depth and a second in the earlier drill hole at 4000 m depth. The idea was to find out whether the buried electrode was close to a high‐conductivity layer of regional extent. The surprising result was that the two apparent resistivity curves measured with the transmitter spread perpendicular and parallel to the NNW striking very highly conductive fracture zones are almost overlapping, even though these fracture zones are the cause of a strong structural anisotropy of the apparent resistivity measured with magnetotellurics. Such a strong anisotropy should also show up in the buried electrode experiment except when a high‐conductivity layer close but above the buried electrode at 9000 m depth is introduced in the model, As a result, the interpretation of this experiment suggests a NE dipping electrically conductive fault system soling out into a high‐conductivity horizontal layer at 7–8 km depth. The conductivity is increased due to graphite and high‐salinity fluids, in a depth near the fossil Cretaceous brittle‐ductile transition zone for quartz‐rich rocks.

Organic static induction transistor for display devices

Organic static induction transistors (SITs) for display devices are proposed and the basic electrical characteristics of the SITs are investigated. The organic SITs, using a copper phthalocyanine (CuPc) evaporated film as an active layer, have a layered structure of Au (drain)/CuPc/Al (gate)/CuPc/Au (source)/glass. The electrical characteristics show that the current flow from the source to drain electrodes is controlled by relatively low gate voltages. Furthermore, excellent characteristics such as a high current density of approximately 4 mA/cm 2 and high-speed operation of less than 0.25 ms are realized by applying a buried Al grid electrode as the Schottky gate.

Simulation of interference patterns in solid-state biprism devices

In this article, we present simulation results for the solid-state biprism, a recently proposed vertical ballistic electron wave interference device. The simulations are performed using a simple simulation method, similar to optical ray tracing. With it, the positions of the fringes are calculated faster than by a direct solution of the Schrödinger equation, and nonetheless it is demonstrated that the same fringe spacing is obtained as from the direct solution. Using this method, the interference for an arbitrary potential structure can be calculated, and in this article, results for the potential produced by three buried thin-metal electrodes are presented. It is shown that by applying voltages to the electrodes asymmetrically, the interference pattern can be swept over a single thin-detector electrode, and that it can in this way be detected experimentally. It is also demonstrated that a relatively large energy distribution of the injected hot electrons does not significantly degrade the performance of the device, whereas the influence of possible incident lateral k vectors must be reduced.

Fabrication of ohmic contacts to buried diamond layers using Pt layer in the diamond chemical-vapor-deposition process

Electrical contacts to a buried chemical-vapor-deposited (CVD) diamond layer can be accomplished using a process in which Pt columns automatically grow from the buried layer to the diamond surface by diamond overgrown on a thin Pt film. Hall effect measurements were employed in a temperature region from room temperature to 450 °C to investigate and compare transport properties of a buried B-doped homoepitaxial diamond film with such Pt column electrodes before and after the overgrowth of the upper layer. A useful ohmic contact to the B-doped CVD diamond interlayer was formed by this type of buried electrodes.

TCE treatment pasta-bilities.

Monsanto's "Lasagna" process uses layers of treatment zones spaced between buried electrodes to remove trichloroethylene (TCE) from contaminated soil and groundwater. TCE is used primarily as a metal degreaser as well as in products such as dyes, printing ink, and paint. TCE can eventually make its way into the environment and is prevalent in the water and soil of industrialized nations. Although TCE breaks down in a few days when released into the atmosphere, it degrades much more slowly in soil, taking months or years. Moreover, it is often broken down by microbes into toxic substances such as vinylidene chloride (a suspected human carcinogen) and vinyl chloride (a known human carcinogen). The Lasagna process is based on the principle of electro-osmosis, in which an electric current draws water from low--permeability soils such as clays, silts, and fine sands. To remove TCE from contaminated soils, Monsanto scientists added layers of filtering media, which attack the contaminant as it is pulled from electrode to electrode. The technology has been tested at the Paducah Gaseous Diffusion Plant in western Kentucky, where it removed over 98% of TCE from contaminated soil.

Highly efficient electron emission from diode-type plane emitters using chemical-vapor-deposited single-crystalline diamond

A highly efficient electron emitting diode with a flat emission surface has been fabricated using a 600 nm single-crystalline diamond film homoepitaxially grown on high-pressure synthesized (100) diamond by means of chemical-vapor deposition and ion-implantation techniques. The emitter contains a buried injection electrode layer and a hydrogenated diamond surface. When driving voltages ranging from 0.3 to 1.1 kV were applied between them, very efficient electron emissions were observed. The emission efficiency, defined as the ratio of the emission current to the injection diode current, reached 100% for emission currents on the order of 10−7 A and did not significantly depend on the currents.

Lithium niobate integrated-optic voltage sensor with variable sensing ranges

A lithium niobate integrated-optic voltage sensor with variable sensing ranges is realized, which consists of a Mach-Zehnder interferometric wave-guide with an array of buried electrodes. The buried electrodes are fabricated by wet etching of proton-exchanged lithium niobate. In this sensor, the sensing range is almost linearly controlled by simply changing the electrode gap and length. Thus the whole sensing range is effectively extended by integrating a number of electrodes which give different sensing ranges. A sensor with three variable sensing ranges is fabricated and its overall sensing range covers 7 mV to 400 V.

Superconducting field effect transistors with YBa 2Cu 3O 7− x/SrTiO 3/YBa 2Cu 3O 7− x trilayer structure

A new superconducting field effect transistor (SuFET) with symmetrical gate structure of YBa 2Cu 3O 7− x /SrTiO 3/YBa 2Cu 3O 7− x (YBCO/STO/YBCO) was fabricated by adopting both the contact structure of buried YBCO electrodes and buried isolation structure. The T c of the YBCO (100 nm)/STO (200 nm)/YBCO (5 nm) structures exceeded 50 K. The I– V characteristic of gate insulator STO was symmetric. The adoption of YBCO as electrode greatly improved T c values of ultrathin YBCO channels without buffer layers. We succeeded in SuFET operation with a YBCO channel of two-unit-cell thickness. The modulation factor exceeded 20%. The number of YBCO unit cell dependence on T c indicates that the degradation is negligible at the STO/YBCO interface.

Simultaneous Operation of Superconducting Field Effect Transistors

A new process was developed for preparing four superconducting field effect transistors (SuFET's) on a substrate. This process yielded the gate structure of YBa2Cu3O7-x /SrTiO3/YBa2Cu3O7-x (YBCO/STO/YBCO) and the contact structure of buried YBCO electrodes. The average T c of the YBCO (100 nm)/STO (200 nm)/ YBCO (5 nm) structures was 49.7 K and the I–V characteristics of gate STO were symmetric. The temperature dependence of transconductance was larger compared with other SuFET's reported to date. Furthermore, we confirmed the operation of all the SuFET's on one substrate and two adjacent SuFET's connected in series. This device fabrication process also led to improved T c values of ultrathin YBCO channels.

Characteristic of a broadband Ti:LiNbO3 optical modulator with buried electrodes and etched grooves in the buffer layer

Traveling wave Ti:LiNbO3 Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO2 buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained.

Laser patterning of thin-film electrochemical gas sensors

We have patterned a CO2 thin film electrochemical sensor using Xe laser ablation of Pt, Nasicon and Na2CO3 thin films. A thin metallic absorbing layer on Nasicon is used to achieve reproducible ablation of the ionic conductor with no piercing of the buried Pt electrode. Processing conditions are 10 J/cm2 pulses with a scanning velocity of 500 μm/s for Pt and 6.3 J/cm2 pulses with a scanning velocity of 100 μm/s for Nasicon. Nasicon is ablated in the form of flakes suggesting an ablation in the solid phase. Fabrication of an integrated heating element and a micro-thermometer by laser ablation is also presented.

A comparison of exact and quasi-static methods for evaluating grounding systems at high frequencies

Recently, it has been suggested that traditional quasi-static methods for evaluating power network grounding systems are not valid at high frequencies. However, the conditions under which exact full wave theory must be used have not been established. In this paper, exact full wave and quasi-static methods are used to evaluate touch and step potentials of a simple ground stake. It is shown that a sufficient condition for quasi-static theory to be valid is if the size of the buried electrode is less than one-tenth of a wavelength in the earth.

Grounding resistance of buried electrodes in multi-layer earth predicted by simple voltage measurements along each surface-a theoretical discussion

A power system protection earth is modeled as an inhomogeneous conducting medium with multiple horizontal layers. For known layer conductivities and thickness, the voltage distribution and grounding resistance have been computed efficiently using an equivalent image method. In this paper, the reverse sequence is proposed. Without explicitly knowing the layer conductivities, thickness and number of layers, the equivalent images are determined by the voltage measurement results along the earth surface. Then these images are linearly translated to compute the underground voltage profiles and grounding resistance of buried electrodes. Such surface measurements are simple and inexpensive, and should give very accurate results based on the experience of applying these images in the microwave area. >

SOI 'SIMOX'; from bulk to surface micromachining, a new age for silicon sensors and actuators

Abstract Separation by ion implantation of oxygen (SIMOX), today an industrial 'silicon on insulator (SOI) substrate', allows a number of improvements for silicon sensors or actuators. For piezoresistive detection, the silicon top layer (0.2 μm thick) is used as an active material with the excellent properties of the single-crystalline silicon. Thanks to its very good electrical insulation from the substrate, high temperature sensors (up to 300 °C) with low noise and high dynamic range can be obtained. These devices are generally and preferably made by bulk micromachining for high performance sensors. Another important aspect of this substrate is its ability to get, by epitaxy, a high mechanical quality silicon layer (thickness > 10 μm) for surface micro-machining and the electronic circuits integration for smart sensors. Capacitive detection seems to be most suitable for miniaturised and cheaper surface microstructures. In the case of sensors (pressure or acceleration) with the detection axis perpendicular to the substrate, a higher capacitance variation is obtained due to the thinness of the SiO 2 sacrificial layer (0.4 μm). This high sensitivity allows a reduction of the sensor area. For acceleration sensors with the detection axis parallel to the substrate, the high thickness of the epitaxial silicon layer allows high stiffness ratio which reduces the sticking effect. Moreover, deep dry etching of silicon, which is today a mature technology, provides higher capacitance variation. The last but not the least advantage is the possibility, thanks to the low thickness of the superficial stack (0.6 μm for both layers), to get localised buried electrodes by deep implantation before the epitaxial process. With this extra electrode, the parasitic capacitance can be reduced and the characteristics of the sensor or the actuator improved.

A novel technology for a-Si TFT-LCD's with buried ITO electrode structure

A novel process technology for a-Si TFT-LCD's with the buried ITO electrode (BI) structure was developed and applied to 10-in-diagonal LCD panels. By employing the BI structure, an aperture ratio of 29% was achieved in high resolution panels with a pixel size of 192 /spl mu/ and the pixel defect density was reduced to about one third of the conventional structure. The defect reduction effect of the BI structure was also confirmed theoretically. The BI structure provides significant advantages for high-performance TFT-LCD's.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigation of capacitive coupling voltage contrast using a specimen charging model

Abstract The capacitive coupling voltage contrast effect has been simulated using a versatile charge simulation program. Simulation shows that the potential distribution of the irradiated passivation surface depends on the size and the shape of the beam profile. When the width of the beam spot is equal to or less than the width of the buried electrode and the electrode voltage is positive, a negative charge ring is formed around the irradiated spot. As a result of this charge ring, the irradiated spot above an electrode with non-positive voltage need not charge to a positive equilibrium potential. Differential charging of passivation surface enhances the lateral field on the surface. The field is highest during voltage switching, its amplitude depends on the voltage swing on the electrode and can be several times stronger than the field existing on the uncharged surface. The field strength reduces slightly at equilibrium.

Fabrication of 30 nm inter-electrode gap co-planar tunnel junctions with buried electrodes

Co-planar tunnel junctions with a gap length in the 30 nm range have been fabricated using a 20 keV scanning electron microscope and a Au-Pd lift-off. The junction electrodes are less than 200 nm in width and are buried in the SiO 2 substrate. This makes the gap surface accessible for atomic force microscope characterization and for local modification

Application of geoelectric methods using buried electrodes in exploration and mining : Draskovits, P; Simon, A Geophys ProspectV40, N5, July 1992, P573–586

Various geoelectric methods which have been deveIoped and applied in the last 10-20 years in ELGI are discussed. These methods which use buried electrodes are: hole-to-surface gradient mapping to detect bauxite deposits in sinkholes below a resistive screening layer; in-mine gradient profiling to map the basement topography below galleries; and the hole-tosurface version of geoelectric layer tracing to find outcrops of mineralized zones penetrated by drillings. Data processing procedures have been developed on the basis of common concepts and hypotheses to link theoretical models with geological structures. The objects investigated are determined as the difference between the theoretical models and geological structures.