Pull-out Voltage Research Articles

The Effect of Surface Chemistry on MEMS Stiction in an Ultralow-Humidity Environment

The susceptibility of microelectromechanical systems (MEMS) devices for stiction, treated with two different antistiction coatings, is investigated in ambient and ultralow-humidity environmental conditions. Wafer-level testing with a pull-in/pull-out voltage technique and a current compliant source was used to detect stiction on capped and uncapped wafers. Historically, the devices coated with a phenyl siloxane coating and capped in a dry nitrogen environment failed due to stiction at the wafer level with pull-in/pull-out tests as well as the packaged parts during tap testing. Although the uncapped devices did not show stiction at ambient humidity using the pull-in/pull-out detection technique, successive drops in the pull-out voltage were detected as the conditions of the test control chamber became drier. The sensitivity of the stiction performance to environment conditions was eliminated when the MEMS devices were coated in a fluorinated silane coating. The results are explained in terms of wetting angle and surface chemistry behavior of the coatings, resulting in improved hydrophobicity, thus mitigating adhesive capillary forces.

Experimental analysis of pull-out voltage of electrostatically actuated microcantilever beam based on contact-stiction model

The effects of stiction forces on the pull-out voltage of electrostatically actuated microcantilever beams have been theoretically and experimentally investigated. An analytical method to estimate the pull-out voltage of microcantilevers under the presence of stiction forces along with electrostatic forces has been presented based on Euler Bernoulli beam model. The stiction effects of van der Waals force and Casimir force have been incorporated along with the electrostatic force in the Euler Bernoulli equation and the results have been numerically evaluated to predict the pull-out voltage. The theoretical results have been compared with experimental results through experimental investigation of the voltage transfer characteristics of the cantilever.

Charging in Dielectricless Capacitive RF-MEMS Switches

This paper presents results on high lifetime RF microelectromechanical (RF-MEMS) dielectricless capacitive switches. Using air gap variation only, these RF MEMS capacitive switches achieve a capacitance ratio of 9, associated with small residual charging. The reliability of the switch has been studied, pull-in and pull-out voltages shifts have been observed, modeled and validated with good agreement between model and measurements for a switch held for one month in the down state. The dependence of charging mechanism to the biasing signal is also presented by applying unipolar and bipolar waveforms with different duty cycles. Charging can be modeled using a simple Curie-Von Schweidler equation. It is shown that the duty cycle of the bias signal is strongly accelerating switch failure, and that using bipolar signals improves the lifetime of these switches by several orders of magnitude. The projected lifetime of current RF-MEMS dielectricless switches held in the down state using bipolar signals is several tens of years.

A GSM/EDGE/WCDMA Adaptive Series-LC Matching Network Using RF-MEMS Switches

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> To preserve link quality of mobile phones, under fluctuating user conditions, an adaptively controlled series-LC matching circuit is presented for multi-band and multi-mode operation. Following a bottom-up approach, we discuss the design of an RF-MEMS unit cell for the construction of a 5-bit switched capacitor array. To reduce dielectric charging of the RF-MEMS devices their average biasing voltage is minimized by applying a bipolar waveform with a small high/low duty-cycle obtained from a high-voltage driver IC. RF-MEMS capacitive switches are applied because of their high linearity, low loss, large tuning range, and easy control in the discrete domain. Application specific RF-MEMS pull-in and pull-out voltage requirements are derived. An impedance phase detector is used to feed mismatch information to an up-down counter providing robust iterative control. The measured MEMS array capacitance tuning ratio is almost a factor 10. Module insertion loss is 0.5 dB at low-band and high-band. Harmonic distortion is less than <formula formulatype="inline"><tex Notation="TeX">${-}\hbox{85~dBc}$</tex> </formula> at 35 dBm output power and the EVM, measured in EDGE-mode, is less than 1% at 27 dBm . The adaptively controlled module, connected to a planar inverted-F antenna, shows desired impedance correction. For extreme hand-effects the maximum module impedance correction at 900 MHz is <formula formulatype="inline"><tex Notation="TeX">$-75j \Omega$</tex></formula>. </para>

Analytical Modeling of the Suspended-Gate FET and Design Insights for Low-Power Logic

An analytical model for the suspended-gate field-effect transistor (SGFET), dedicated to the dc analysis of SGFET logic circuits, is developed. The model is based on the depletion approximation and expresses the pull-in voltage, the pull-out voltage, and the stable travel range as a function of the structural parameters. Gate position is explicitly expressed as a function of the gate voltage, thus enabling the convenient integration of the analytical SGFET relationships into the standard MOSFET models. Starting from the new SGFET model, the influence of the mechanical hysteresis on the circuit steady-state behavior is discussed, the potential of using the SGFET as an ultra-low power switch is demonstrated, and the operation of the complementary SGFET inverter is analyzed.

Estimation of Stiction Force From Electrical and Optical Measurements on Cantilever Beams

In this paper, we estimate the stiction force from electrical (current-voltage) measurements on surface micromachined polysilicon cantilever beams. A bias voltage was applied between the beam and the substrate. At the pull-in voltage, the beam collapsed to the substrate and the current rose rapidly from zero. Similarly, at the pull-out voltage during bias sweep back, the current dropped rapidly to zero when the contact between the beam and the substrate was broken. An analytic model for the stiction force was developed in terms of the pull-in and pull-out voltages and was used to estimate a stiction force of about 70 nN from the measured electrical characteristics. This method of characterization is suitable for use in packaged devices. An analytic model was developed to estimate stiction force from optical surface-profile measurements of the curvature of long collapsed cantilever beams in a cantilever-beam array, in the absence of any electrostatic actuation. The force per unit length of about 14 nN/m thus obtained was used to compare the effects of surface roughness on stiction.

Non-contact electrostatic microactuator using slit structures: theory and a preliminary test

A new type of electrostatic microactuator with pull-in and pull-out behaviors has been presented based on nonlinear electrostatic force acting on a slit structure. Theory for the microactuator has also been developed to understand the nonlinear behaviors of the microactuator when a voltage is applied to the microactuator. Using dimensional analysis and finite element analysis (FEA), the nonlinear electrostatic force was investigated and was formulated in a simple closed-form equation whose coefficients are functions of the geometry of the microactuator. Afterwards, a force balance equation of the microactuator was set up and then an equation for the height of the movable structure at a voltage was derived. Theoretical analysis shows that without mechanical contact the microactuator suffers from a pull-out as well as a pull-in phenomenon. When the movable grating is spaced by a distance larger than a minimum distance, the pull-in and pull-out phenomena occur at the corresponding pull-in and pull-out voltages, respectively. In a preliminary experiment using a microactuator made of a 1.5 µm thick polysilicon, the pull-in voltage is measured to be 19 V. As a new type of electrostatic microactuator, microactuators using slit structures have potential applications in micro- and nano-systems such as actuators with a large travel range, micromirrors, variable capacitors, tunable RF filters and microaccelerometers.

An intelligent bipolar actuation method with high stiction immunity for RF MEMS capacitive switches and variable capacitors

We propose an intelligent bipolar actuation (IBA) method for electrostatic actuators, which can suppress stiction induced by dielectric charging. The high stiction immunity is achieved by flipping the bias voltage polarity depending on the pull-out voltage, thereby restricting the amount of charge stored in the dielectric film.

Principles of space-charge based bi-stable MEMS: The junction-MEMS

We propose a theoretical investigation of a new principle of bi-stable MEMS based on the remnant electrostatic force generated by the space-charge density that builds up when two semiconductors, having different doping densities, are brought into contact. Following a physical description of the device, a complete analytical formulation of some key parameters such as the pull-in and pull-out voltages could be obtained. The model reveals that both closed and open configurations of the switch MEMS can be stable states at zero applied voltage. The impact of the different technological parameters is also discussed in details, supporting that the so-called junction-MEMS might be an interesting alternative to address bi-stability in MEMS, still remaining fully compatible with the standard microelectronics technologies.

Temperature study of the dielectric polarization effects of capacitive RF MEMS switches

This paper investigates both theoretically and experimentally the dielectric charging effects of capacitive RF microelectromechanical system switches with silicon nitride as dielectric layer. Dielectric charging caused by charge injection under voltage stress was observed. The amphoteric nature of traps and its effect on the switch operation were confirmed under both positive and negative control voltages. It has been confirmed that charging is a complicated process, which can be better described through the stretched exponential relaxation. This mechanism is thermally activated with an activation energy being calculated from the temperature dependence of the capacitance transient response. The charging mechanism, which is responsible for the pull-out voltage and the device failure, is also responsible for the temperature-induced shift of the capacitance minimum bias.

A comprehensive model to predict the charging and reliability of capacitive RF MEMS switches

Reliability issues currently hamper the commercialization of capacitive RF MEMS switches. The most important failure mode is parasitic charging of the dielectric of such devices. In this paper we present an improved analytical model that enables us to calculate and understand the effect of insulator charging on the behavior of capacitive RF MEMS switches, and to describe the way they fail, and their reliability. Emphasis is placed on a shift of the pull-out voltage to predict failures. Tests with capacitive RF MEMS switches have been performed that validate the most important features of the model.