Robert V. Wright

Wafer-Level Transfer Technologies for PZT-Based RF MEMS Switches

We report on wafer-level transfer technologies to integrate PZT-based radio frequency (RF) microelectromechanical-systems switches on CMOS. Such heterogeneous integration can overcome the incompatibility of PZT material with back-end-of-the-line (BEOL) CMOS technology. The PZT stack and the transfer process have been optimized to avoid degradation of the PZT actuators during the transfer. In particular, we have optimized the seed layer for the growth of highly oriented PZT on a patterned TiO2-Pt layer, optimized the electrodes structure, and developed an Al2O3 capping layer to prevent degradation of PZT during the transfer process. A full wafer-level transfer process and a selective transfer technology allowing the distribution of RF switches from one source wafer to many receiving wafers has been demonstrated. The latest transfer process demonstrated exhibits great potential for cost optimization of wafer-level transfer of microdevices. In a separate experiment, we have demonstrated the BEOL CMOS compatibility of our integration technique. Switch characterization showed insertion loss of less than 0.5 dB and an isolation better than 30 dB for the 0.4- to 6-GHz frequency range with 15-V actuation voltage.

Low-temperature CMOS-compatible 3D-integration of monocrystalline-silicon based PZT RF MEMS switch actuators on rf substrates

This paper presents a low temperature (200°C) CMOS-compatible fabrication process for integrating high-temperature deposited lead zirconate titanate (PZT) on thin film monocrystalline-silicon piezoelectric actuators, onto an RF substrate, and successful demonstration of this process for fabrication of metal-contact RF-MEMS switches. The patterned PZT/silicon multi-layer stack is transfer-bonded from a silicon-on-insulator (SOI) donor wafer to an AF-45 glass RF substrate using adhesive wafer transfer bonding. Furthermore, several strategies have been investigated to drastically reduce the post bonding misalignment created by the shear forces between the bonding chucks during wafer bonding.

Growth and high frequency characterization of Mn doped sol-gel PbxSr1-xTiO3 for frequency agile applications

In pursuit of thin film ferroelectric materials for frequency agile applications that are both easily adapted to large area deposition and also high performance, an investigation has been carried out into sol-gel deposition of 3% Mn doped (Pb0.4Sr0.6)TiO3. Large area capability has been demonstrated by growth of films with good crystallinity and grain structure on 4 in. Si wafers. Metal-insulator-metal capacitors have also been fabricated and development of an improved de-embedding technique that takes parasitic impedances fully into account has enabled accurate extraction of the high frequency dielectric properties of the PbxSr1−xTiO3 films. Practically useful values of e∼1000, tan δ∼0.03, and tunability ∼50% have been obtained in the low gigahertz range (1–5 GHz). Peaks in the dielectric loss due to acoustic resonance have been modeled and tentatively identified as due to an electrostrictive effect with an electromechanical coupling coefficient of ∼0.04 at an electric field of 240 kV/cm which is potenti...

Tunable Bandstop Resonator and Filter on Si-Substrate with PST Thin Film by Sol-Gel Deposition

Tunable bandstop resonators and filters are fabricated and measured. Lead strontium titanate (PST-Pb0.4Sr0.6(Ti1-x Mnx)O3) thin film on a high-resistivity Si substrate is used for an application of low loss tunable circuits at microwave frequency band. Parallel plated PST varactors tune resonators and 3-pole bandstop filters which resonate at the center frequency of 4.23 and 7.1 GHz and its maximum rejection is more than 13.8 dB at the stop band while the insertion loss at the pass band is less than 3 dB.

Materials specification for MCM-D decoupling capacitors using PZ, PZT, PLZT and BST dielectrics

Abstract The desired electrical properties of decoupling capacitors for use in an existing MCM-D process have been defined. Two types of dielectric have been investigated, sol-gel deposited P(L)ZT and dual ion beam sputtered (DIBS) BST. Their electrical properties have been measured and compared against this target. Decoupling capacitors have been fabricated and integrated with an MCM-D process, the resulting processing issues are discussed.

RF MEMS Zipping Varactor With High Quality Factor and Very Large Tuning Range

An RF MEMS zipping analog varactor with a high-permittivity bismuth zinc niobate dielectric has been fabricated and characterized. The varactor can be continuously tuned from 10 to 280 fF, with a very large tuning range of 2700%. By use of gold electrodes to ensure a low series resistance, the high quality factors of 317 and 63 at 1 GHz were measured for the minimum and maximum capacitances, respectively. The self-resonance frequency of the varactor is estimated to be 16.6 GHz at the maximum capacitance and 87.6 GHz at the minimum capacitance. With a small device footprint of 540 × 130 μm2, the zipping varactor is suitable for application in portable reconfigurable RF systems.

Development of micromechanical and optical devices incorporating deposited PZT films

Abstract This paper reports the results of a 3 year Brite-Euram (III) programme aimed at extending the functionality of micromechanical and optical devices utilising both thin and thick film PZT technologies: a oscillatory gyroscope with a resolution of 0.2°/s, signal bandwidth of 30Hz @-3dB and dimensions of 20–25 mm2, a valve-less diffuser micropump capable of 0.05ml/min. and 3.5kPa maximum flow and pressure, a planar waveguide optical switch with insertion loss <1dB and switching time <1msec, and an integrated IR detector array with NETD <100 mK. Cantilever test structures indicate that d31 for these films is ∼70 pC/N. Thinner films, <1μm, have been developed for the integrated IR detector array which have a pyroelectric coefficient ∼250μC/m2/K and FD ∼1.5x10−5 Pa−1/2. Laser crystallization of PZT using a pulsed excimer laser system has been successfully demonstrated. This is particularly significant for integration of PZT with active circuitry where post-processing temperatures must be kept below about 550°C.

Transfer of Functional Ceramic Thin Films Using a Thermal Release Process

Being ferroelectric, piezoelectric, and pyroelectric, lead zirconate titanate (PZT) is one of the most useful and prominent electroceramics and is commonly used as the transduction element of actuators and sensors in microelectromechanical systems (MEMS) and micro-optics [1–6] and in memory devices. [7,8] It is also being explored for new applications such as nanorods, [9] domain physics, [10] and nanodevices. [11,12] Transfer of PZT thin films can allow integration of such films on substrates that are incompatible with the requirements of film deposition. However, transfer of functional ceramic thin films has long been hampered by the difficulty of detaching the film from the growth substrate. [13,14] Here, we describe a transfer process for PZT films grown on Ti/Pt coated Si wafers, where the films are solder bonded onto a target substrate and lifted off in one step, using separation of the PZT–Pt interface by thermal stress. The transferred films show low mechanical damage, ferroelectric hysteresis with an “imprinted” polarization, [15] reduced permittivity, and improved loss tangent.

Lead-Strontium-Titanate varactor-tuned CPW bandstop filter on liquid crystal polymer substrates

This paper presents an investigation of a tunable coplanar waveguide (CPW) bandstop filter with slotted ground structure. Spurious responses resulting from the shapes of resonator and the tuning position have been investigated by EM simulations. As a tuning element, Lead- Strontium- Titanate (PST) varactor chip is deployed. Also, in order to reduce required elements and unwanted spurious, LCP substrates are used as multi-layered laminates. A 2-pole tunable bandstop filter of this type is measured at the center frequency from 905 to 1040 MHz and its maximum rejection is more than 25 dB at the stopband with a wide passband response.

Improvement of Electrical and Mechanical Properties of Inkjet-Printed Ag Tracks by Adding SiO2 to High Loading Ag Inks

Monodispersed Ag nanoparticles with sizes down to 10 nm were synthesised in an aqueous medium. These nanoparticles were then successfully dispersesd up to 45 wt% in aqueous medium with the aid of a copolymer, Pluronic F127. SiO2 nanoparticles were added to the ink formula in order to improve the physical properties of the ink after inkjet printing. The effect of the different SiO2 concentrations in the ink on the adhesion, resistivity and microstructure of the film at several sintered temperatures was investigated. The percentage of the SiO2 added in the ink was responsible for the development of microstructure for the sintered silver films and improving adhesion of the films to the substrate. The addition of SiO2 had also significant effect on improving the conductivity of the films. The conductivity is, though, better when only a small amount of SiO2 was added.