Switch Lifetime Research Articles

A LOW VOLTAGE MEMS STRUCTURE FOR RF CAPACITIVE SWITCHES

A novel structure for the capacitive micromachined switches with low actuation voltage is proposed. In this structure both contact plates of the switch are designed as displaceable membranes. Two structures with similar dimensions and conditions, differing on only the number of the displaceable beams are analytically investigated as well as simulated using ANSYS software. The obtained results indicate about 30% reduction in actuation voltage from the conventional single beam to our proposed double beam structure. The stress on the beam due to the actuation voltage is also reduced increasing the switching life time. The dynamic simulation results in switching time of 6.5μsec compared to the 8.9μsec of the analytical results. It can be implemented by the well established surface micromachining for RF applications.

Reliability modeling of capacitive RF MEMS

The kinetic of dielectric charging in capacitive RF microelectromechanical systems (RF MEMS) is investigated using an original method of stress and monitoring. This effect is investigated through a new parameter: the shift rate of the actuation voltages. We demonstrate that this lifetime parameter has to be considered as a function of the applied voltage normalized by the contact quality between the bridge and the dielectric. We also demonstrate that this phenomenon is related to Frenkel-Poole conduction, which takes place into the dielectric. We finally propose a model that describes the dielectric charging kinetic in capacitive RF MEMS. This model is used to extract a figure-of-merit of capacitive switches lifetime.

Significance of Surface Topography on Performance and Lifetime of MEMS Switches and Relays

AbstractSwitches and relays that have emerged from the microelectromechanical systems (MEMS) technology have the potential to replace traditional solid-state devices due to broader operating temperature range, higher breakdown voltage, and much higher off-state resistance. Interest in MEMS switches and relays has surged recently, principally due to the demonstrated performance in switching radio-frequency signals. However, understanding of the effect of the surface topography on performance and lifetime of these microdevices is rather empirical. Therefore, the objective of this study was to explore the role of surface topography in various physical phenomena encountered at contact interfaces of MEMS switches and relays. Emphasis is given on the dependence of pull-in voltage, electric field, and electrical breakdown on surface topography and interpretation of contact interface phenomena associated with surface erosion and adhesion in the context of surface topography effects. In addition, current obstacles in the study of the influence of the surface topography on the performance of MEMS switches and relays are discussed in light of recent findings.

Smart electrochromic windows (SECWs) for energy management

Smart Electrochromic Windows (SECWs) — the windows for future, are the windows, which by dynamically controlling solar and visual properties in response to exterior environmental conditions and interior needs, can offer visual and thermal comfort along with significant amount of energy saving. They play an increasingly important role in high standards of efficient energy usage and management in new building regulations. Their greatest value is generated if they can respond appropriately in terms of dynamic switching speed, color, lifetime and optical properties and if they can be fabricated cost effectively. This paper presents some of the results of our preliminary attempts made in this direction, in terms of the preparation and salient features of the components of the SECWs developed and the performance characteristics of different prototype SECWs fabricated and their comparison.

Low-actuation voltage RF MEMS shunt switch with cold switching lifetime of seven billion cycles

This paper investigates the performance and lifetime of a metal-to-metal shunt RF MEMS switch fabricated on an SI-GaAs substrate. The switch is a shunt bridge design that is compatible with standard microelectronic processing techniques. The RF performance of the switch includes actuation voltages of less than 15 V, isolation better than 20 dB from 0.25 to 40 GHz, and switching speeds of less than 22 /spl mu/s. Varying the geometry of the switch affects both switching voltage and reliability, and the tradeoffs are discussed. We have developed a cold switching test method to identify the root cause of sticking as a failure mechanism. The switch structure includes separation posts that eliminate sticking failure and has demonstrated lifetimes as high as 7/spl times/10/sup 9/ cold switching cycles. These results show that good reliability is possible with a metal-to-metal RF MEMS switch operated with a low actuation voltage.

High-power photoconductive semiconductor switches treated with amorphic diamond coatings

The mechanical and semiconductor properties of amorphic diamond can be employed to improve the photoconductive semiconductor switch longevity by coating the switch cathode or anode areas or both. In this paper, issues concerning the switch longevity were studied by fabrication and testing the GaAs photoconductive switches treated with the amorphic diamond under different switch configurations, gap settings, and diamond coating thickness. The tunneling of electrons from amorphic diamond to GaAs during the off-state stage of operation provided preavalanche sites that diffused conduction current upon switch activation. A significant improvement in switch lifetime was demonstrated by testing the diamond-coated switch performance in a prototype pulser. Elementary processes involved in conduction of diamond treated switch and other design options such as coating of switch anode area are examined and discussed.

Silicon carbide as electrode material of a pseudospark switch

Through the last years, the pseudospark switch, a low-pressure gas discharge switch with hollow cathode geometry, became established as a promising element of pulsed power technology and a serious alternative to other high-power switches. The use of a novel electrode material silicon carbide yields performance improvements in two main areas. Quenching phenomena, a long-standing problem for several applications, are suppressed completely and the switch lifetime can be distinctly increased, approaching that of thyratrons for operation with high repetition rate. As a crow-bar switch, the lifetime is nearby unlimited due to cold electrode usage. Spatial and temporal resolved spectroscopy revealed new insight into the extraordinary discharge behavior of silicon carbide electrodes. The radial plasma expansion from the central bore hole to the outer electrode regions, forming vesicular shells of different ionization stages of Si and C, are described in detail. The remaining problem, a significant loss of deuterium gas during discharge, has been long-term tested and is assumed to be the outcome of absorption in the silicon carbide electrodes. An envisaged promising remedy is presented.

Photoconductive switch enhancements and lifetime studies for use in stacked Blumlein pulsers

Photoconductive switching of the stacked Blumlein pulsers, developed at the University of Texas at Dallas, currently produces high-power nanosecond pulses with risetimes on the order of 200 ps. The device has a compact geometry and is commutated by a single GaAs switch triggered by a low-power laser diode array. This report presents the progress toward improving the high-gain switch operation and lifetime in stacked Blumlein pulsers. Feasibility of the use of amorphic diamond to enhance the switch operation and longevity is studied. Improvement in switch lifetime was demonstrated by coating the triggered face of a GaAs switch cathode with highly adhesive film of amorphic diamond. Relevant semiconductor properties of amorphic diamond are discussed.

Final results from the high-current, high-action closing switch test program at Sandia National Laboratories

We tested a variety of high-current closing switches for lifetime and reliability on a dedicated 2-MJ, 500-kA capacitor bank facility at Sandia National Laboratories. Interest was in a switch capable of one shot every few minutes, switching a critically damped, de-charged 6.2-mF bank at 24 kV, with a peak current of over 500 kA. The desired lifetime is 24000 shots. Typical of high-energy systems, particularly multimodule systems, the primary parameters of interest related to the switch are 1) reliability, meaning absence of both pre-fires and no-fires; 2) total switch lifetime or number of shots between maintenance; 3) cost. Cost was given lower priority at the evaluation stage because there are uncertainties in estimating higher-quantity prices of these devices, most of which have been supplied before in only small quantities. Cost has more importance in choosing between viable candidates after testing The categories of switches tested are vacuum discharge, high-pressure discharge, and solid-state. Each group varies in terms of triggering ease, ease-of-maintenance, and tolerance to faults such as excess current and current reversal. We tested at least two variations of each technology group. The total number of shots on the switch test facility is about 50000. This paper will present the results from the switch testing. The observed lifetime of different switches varied greatly: the shortest life was one shot; one device was still operating after 6000 shots. On several switches, we measured the voltage drop during conduction and calculated energy dissipated in the switch; we will show these data also.

Design and testing of a rotary arc gap-switch for pulsed power

One of the key issues in pulsed power generation and its application is switch technology. The switches are divided into two categories of opening and closing switches. The most popular closing switches to date are spark-gap switches. The closing switches have a very limited lifetime due to arc corrosion resulting from the pinch effect and localized arc heating [Hare et al. (1975)]. Electrode phenomena in high-current carrying switch and transient phases in intense arcing modes are presented in papers by Prucker and Christiansen (1977) and Lehr et al. (1987). To extend the switch lifetime by minimizing electrode-vaporization, rotary arc gap-switches are investigated in papers by Kumar and Pramanik (1995), Desaulniers-Soucy and Meunier (1995), Gulie and Sloot (1975), and Yasko (1969). In those switches, rotation of the arc can be achieved by providing a rotating magnetic field from outside or by a self-induced magnetic field. Extensive experimental and theoretical investigations on arc characteristics and arc velocities in ring-type spark gaps are reported in papers by Gulie and Sloot (1975) and Yasko (1969). This paper investigates a rotating arc gap (RAG) switch driven by self-induced magnetic field. The physical dimensions, rotating arc speed, arc voltage drop, and its experimental setup are described in detail.

Design considerations for corona-stabilized repetitive switches

Self-closing corona-stabilized switches have been developed to operate at pulse repetition frequencies (PRFs) which extend well into the kilohertz regime. The performance of these devices illustrates that corona-stabilized plasma closing switches are an effective alternative to conventional uniform or quasi-uniform field switches which utilize gas-flow techniques, high gas pressures or both to achieve high-PRF operation. Corona stabilization takes place in electronegative gases such as air and and requires the presence of a highly divergent electrical field. Under dc, or slowly rising charging voltage conditions, a space charge develops around the highly stressed electrode which prevents premature breakdown and allows full voltage recovery to take place. This means that PRFs extending into the kilohertz regime can readily be achieved. Self-firing corona-stabilized switches have been demonstrated to provide PRFs of up to 5 kHz and triggered corona switches have been shown to be capable of operation at 10 kHz. The lifetime of corona-stabilized switches has been demonstrated to approach about shots. The paper describes the design of a corona-stabilized switch, including detailed electrostatic field analysis of the electrode geometry. This analysis was undertaken to establish the effect of the electrode geometry on the field distribution within the switch. The switch design was flexible and allowed a study of the effect of certain parameters on the switching performance. These parameters include the gap spacing, the gas pressure and the profile of the electrodes. The switch was operated under single-shot conditions to establish the breakdown voltage against pressure (V-p) characteristics and in a continuous repetitive mode to assess the PRF operation. The results show that the best repetitive performance is produced using electrodes which generate a high field over a region sufficient to generate a stabilizing corona.

The electrochromic response of polyaniline and its copolymeric systems

Conducting polyaniline (PANI) and its copolymer films of poly(aniline-co- o-toluidine) (PAOT) and poly(aniline-co- o-anisidine) (PAOA) have been electrochemically synthesized. The optical and structural properties of PANI, PAOT and PAOA have been studied using UV-visible absorption and X-ray diffraction techniques. The X-ray diffraction study reveals a crystalline structure for PANI whereas it shows an amorphous structure for PAOT and PAOA conducting copolymer films. Moreover, the switching lifetime, applied voltage, cycle lifetime in the glass/ITO/conducting polymer/HCl/ITO/glass configuration of PANI, PAOA and PAOT have been experimentally investigated. Further, the current transient for coloration and discoloration has been analysed in order to understand the charge transport in conducting polymer and copolymeric systems. It has been shown that PAOA shows better electrochromic response (143 ms) than PANI and PAOT systems. It is believed that the presence of the -OCH 3 group in the PAOA copolymer facilitates the torsional angle between aniline and methoxy aniline. In addition, the effect of HCl acid molarity on the switching response of PAOA conducting copolymer films has been studied.

Repetitively operated plasma opening switch using laser produced plasma

A plasma opening switch using laser produced plasma is successfully operated at repetition rates up to 3.3 pulses per second. It is shown that the switch performance has good reproducibility without any maintenance. Reliability tests indicate that the switch lifetime is limited by the volume of the target material and the lifetime of the energy storage capacitor.

Pulsed characterization of vertical gallium arsenide (GaAs) optically activated switches

This paper presents the results of pulsed characterization experiments conducted on vertical GaAs optically activated switches. The voltage hold-off characteristics, optically activated switching properties and lifetime performance of the switches have been examined. An all solid state system has been used to assess the characteristics of epilayered and switches fabricated from liquid encapsulated Czochralski (LEC) and vertical gradient freeze (VGF) GaAs. Non-epilayered devices have also been fabricated from the former material. A range of voltages have been applied to the different switches, up to a maximum of 6.5 kV for the reverse biased VGF devices. The longest lifetime recorded was shots for a LEC device, in which case no damage was visible to the switch. Lifetimes of shots were also observed for the forward-biased devices. A simple model of the voltage dropped across the switch during closure has been developed which assisted in the reduction of the switch `on' resistance. Lifetime and post mortem studies suggest that, in these experiments, the switch closure was due to a single filament. It is concluded that operating a switch with more than one filament, or ensuring that a single filament does not occur in the same position twice, is an effective method for increasing device lifetime.

The characteristics of pulsed hollow cathode discharges used for pseudospark switch triggering

The complex interaction between the trigger discharge and the main switch discharge in high-power gas discharge switches influences both the switching characteristics, and the switch and trigger lifetime. Any attempts to improve either of these parameters has to take into account the pressure and geometry dependence of a particular trigger geometry. Yet, although not very intensely investigated in detail for this particular purpose, pulsed hollow cathode discharges are commonly used for low-pressure gas discharge triggering as in pseudospark switches. Measurements of the electron current flowing to the cathode backplane of a pseudospark switch from the pulsed hollow cathode trigger discharge show that maximum current densities are peaked around the symmetry axis of the trigger electrode, an effect which is more pronounced at low pressures. Delayed (and slowed-down) increase of the current density at larger radii leads to increasing delay and jitter, provided the trigger coupling holes in the cathode backplane are located off-axis. The electron current density increases with decreasing diameter of the trigger electrode, and with increasing pressure of the working gas. In addition, it is shown that a preionization (keep-alive) current in the trigger electrode region shows a distinct influence on the trigger current distribution, proving that there exists an optimum keep-alive current depending on the geometry and gas pressure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pseudospark switches-technological aspects and application

We report results of the development of fast closing switches, so-called pseudospark switches, at Erlangen University. Two different parameter regimes are under investigation: medium power switches (32 kV anode voltage, 30 kA anode current and 0.02 C charge transfer per shot) for pulsed gas discharge lasers and high power switches (30 kV anode voltage, 400 kA anode current and 3.4 C charge transfer per shot) for high current applications. The lifetime of these switches is determined by erosion of the cathode. The total charge transfer of devices with one discharge channel is about 220 kC for the medium and 27 kC for the high power switch. At currents exceeding 45 kA a sudden increase in erosion rate was observed. Multichannel devices are suited to increase lifetime as the current per channel can be reduced. Successful experiments with radial and coaxial arrangements of the discharge channels were performed. In these systems the discharge channels move due to magnetic forces. A skilful use of this phenomena will result in a considerably increase of switch lifetime. Multigap devices enable an increase of anode voltage. A three gap switch has run reliably at an anode voltage of 70 kV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ferroelectric PbZrxTi1-xO3 Thin Films Grown by Organometallic Chemical Vapor Deposition

AbstractFor the successful integration of ferroelectric thin films in IC technology, there is a need for a deposition technique capable of growing homogeneous layers at high growth rates over large-area structured substrates. Organometallic chemical vapor deposition (OMCVD) is a promising technique for meeting these demands.Ferroelectric layers of PbZrxTi1-xO3 (PZT) were grown by OMCVD on Pt-coated 10 cm diameter Si-substrates using the precursors tetra-ethyl-lead, tetra-iso-propoxy-titanium and tetra-tertiary-butoxy-zirconium at 700 °C without any post anneal. At this temperature the layers are single phase and highly (h00) and/or (00l) oriented. The layers show good ferroelectric switching properties with high remanent polarizations, but also with high coercive field strengths. Fatigue measurements are presented for these OMCVD grown PZT layers. The layers have a switching lifetime exceeding 1011 cycles at a switching amplitude of 5 V.

Giant discrete resistance fluctuations observed in normal-metal tunnel junctions.

Giant discrete resistance fluctuations are reported in large (50\ifmmode\times\else\texttimes\fi{}50 \ensuremath{\mu}${\mathrm{m}}^{2}$) tunnel junctions of Au-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$-Au over the temperature range 4--140 K, with applied dc bias voltages of 0--2 V. The fluctuations are believed to result from single electrons trapped on defect sites within the insulating barrier of the tunnel junction. The temperature and bias-voltage dependence of the characteristic switching lifetimes of these fluctuations have been measured, and departures from previously reported behavior are observed.

Anomalous behavior of discrete resistance fluctuation lifetimes in novel metal insulator-metal tunnel junctions

Measurements are reported of the switching lifetimes of the discrete resistance fluctuations in AuAl 20 3Au tunnel junctions which have small Al particles randomly embedded within the insulating barrier. The tunnel junctions are 50×50 Pin 2 and the Al particles are nominally disk-shaped with thickness about 30Å and radius 500Å. Tunnel M-I-M junctions which do not contain embedded metal particles typically have switching lifetimes that decrease exponentially with applied d.c. bias voltage. However, we have found that the presence of embedded particles leads to anomalous behavior, in which the switching lifetimes increase with applied bias voltage. We ascribe this behavior to the interaction of defects with the charge state of the embedded Al particles.

Influence of 3-4 Substitutions On Properties of Five Membered Polyheterocycles

Abstract Thin films of 3-4 substitued 5-membered polyhetero-cycles derived from pyrrole and thiophene have been electro-chemically synthetized, showing reversible electrochemical oxydation and reduction processes, and conductivities varying between 10−4 and 102 ω−1 · cm. The absorption spectra of their doped and undoped states, their switching time and lifetime make some of these polymers interesting for electrochromic applications.