Evaluation of platinum as a structural thin film material for RF-MEMS devices

Abstract

Surface micromachined metal armatures are commonly used for MEMS applications of which RF-MEMS is the most well known. In most cases metals with a high conductivity, such as aluminum or gold, are used. These metals often have a low melting point and therefore have a low thermal stability and show plastic deformation of the structures at relatively low temperatures (<200 • C). High melting point metals, such as platinum, are expected to show plastic deformation only at higher temperatures which makes them interesting for use as a structural layer in RF-MEMS devices. In this paper, we present a technology to realize suspended platinum structures by means of surface micromachining. An improved lift-off process allows patterning 1 μm Pt films on a polyimide sacrificial layer. A comparison of the characteristics and armature resonance frequencies between RF-MEMS switches with Pt armatures and AlCu 0.5% alloy armatures reveals an increased thermal stability for the former up to at least 250 • C. This enables zero-level packaging of switches at relative high temperatures without affecting their performances. The lower conductivity of Pt compared to AlCu 0.5% does not lead to a significant increase in RF losses. Implementing AlN as a dielectric material, the Pt-based capacitive shunt switches reported in this paper showed lifetimes in excess of 5×10 7 cycles under standard testing conditions.

Excitation functions of deuteron-induced nuclear reactions on natural platinum up to 24 MeV

“…Due to its favorable physical and chemical properties, platinum and its alloys are widely used in automobile and petroleum industries as catalytic converters, in laboratory equipment as electrical contacts and electrodes, in ships, pipelines and steel piers as platinum-based anodes, in resistance thermometers, hard disk drive coatings, fiber optic cables, medical instruments, collimators and target backings [1]. It is now finding increasing applications as a suitable structural thin film material due to its stability at very high temperatures, excellent corrosion and wear resistance characteristic [2].…”

Material Selection of Rf-Mems Switch Used for Reconfigurable Antenna Using Ashby's Methodology

“…The beam over the electrode acts as a parallel plate capacitor. When the switch beam is in upstate, the transmission line experiences a small capacitance, and when it is in down state, transmission line experiences a high capacitance [12]. But these switches have their limitations however.…”

“…where I is the current in the switch beam, and R is the beam resistance which is given by [13] R = βρL 4tw (12) where β is a constant and related to the current crowding into the membrane, and ρ is electrical resistivity of the beam. From the Equations (11) and (12), we can conclude that power loss in beam structure is directly proportional to the electrical resistivity of the bridge material.…”

“…Through literature review [11][12][13][14] it has been observed that the possible materials used for bridge material for fixed-fixed beam capacitive shunt switch are gold, aluminum, platinum, molybdenum, copper, nickel, alumina, and silicon nitride. In this study, the key material indices considered for MEMS capacitive switch are Young's modulus, electrical resistivity, Poisson's ratio, thermal expansion coefficient, and thermal conductivity.…”

Platinum–zirconium composite thin film electrodes for high-temperature micro-chemical sensor applications

“…Thin films of noble metals (platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh)) have widespread applications in various devices such as electrodes for chemical and electromechanical sensors and devices [1][2][3][4][5]. In addition, these noble metal films have found applications in high-temperature sensor applications as the elements for micro-hot plates and electrodes for structural monitoring sensors and thermocouples for harsh-environment energy applications (such as gas turbines and fuel cell systems operated at >500 • C) [6][7][8][9][10][11][12][13][14][15].…”