Paul H. Kobrin

Thin film ZnO based bulk acoustic mode filters

We have used thin film ZnO bulk mode resonators on an acoustically reflecting solid glass substrate to produce a variety of filters in the 1-3 GHz frequency bands. Power handling is large (>2W). Overall filter dimensions are very small (/spl sim/1 mm), while lithography requirements are undemanding (>10 /spl mu/m). A range of ladder filters has been produced with an average rejection to insertion loss ratio of /spl sim/10. Monolithic inductors have also been used to improve characteristics over specified bands.

High performance microwave air-bridge resonators

We have used pulsed laser deposition and a dry release process to produce freestanding zinc oxide films for bulk mode microwave acoustic resonators. Laser assisted deposition is used to produce ZnO films with very low (slightly tensile) stress at temperatures below 200/spl deg/C. They have a high degree of orientation, C axis X-ray 1/2 width /spl sim/0.24/spl deg/, resistivity greater than 10/sup 10/ ohm cm and loss tangent below 0.01 at 10 MHz. Resonators with Qs of over 350 with K/sub em/ of 0.22 at 1.5 GHz have been produced. An air-bridge process has been used to produce undistorted freestanding membranes up to 400 /spl mu/m sq., with single mode resonance characteristics. The use of an inorganic sacrificial layer and a dry release etch avoids the problem of surface tension that occurs in wet chemical etching, resulting in high yield. The process also allows for on-wafer frequency trimming. Multipole band pass filters have been designed based on the discrete resonator results, and have been fabricated using this process. A rejection of 28 dB and an insertion loss of -7 dB have been achieved. The high yield and good uniformity make this a practical, low-cost process for producing complex multipole filter structures suitable for 1-3 GHz mobile communications.

Dual frequency liquid crystal devices for infrared electro-optical applications

A dual frequency liquid crystal (DFLC) can be field-driven towards its unperturbed state, which dramatically reduces the overall electro-optical response time. DFLC materials with sub-millisecond switching speed are being used in infrared electro-optical devices at wavelengths up to 3 microns. The performance of devices such as tunable half-wave plates and optical phased arrays in agile beam steering devices, and wavefront controllers for adaptive optics are described. Device issues discussed include drive schemes, field of view, reflective direct drive backplane, infrared-transparent conductors, and antireflection coatings.

Sorbent coatings for nitroaromatic vapors: applications with chemical sensors

The solubility properties of a series of nitroaromatic compounds have been determined and utilized with known linear solvation energy relationships to calculate their sorption properties in a series of chemoselective polymers. These measurements and results were used to design a series of novel chemoselective polymers to target polynitroaromatic compounds. The polymers have been evaluated as thin sorbent coatings on surface acoustic wave (SAW) devices for their vapor sorption and selectivity properties. The most promising materials tested, include siloxane polymers functionalized with acidic pendant groups that are complimentary in their solubility properties for nitroaromatic compounds. The most sensitive of the new polymers exhibit SAW sensor detection limits for nitrobenzene and 2,4-dinitrotoluene at 3 parts per billion (ppb) and 235 parts per trillion (ppt) respectively. Optimized polymers exhibit low water vapor sorption, and rapid signal kinetics for nitrobenzene, reaching 90% of signal response in 4 seconds. Studies with an in-situ infra-red spectroscopy technique are used to determine the mechanism of interaction between nitroaromatic compounds and the chemoselective polymer.

Dual band adaptive focal plane array: an example of the challenge and potential of intelligent integrated microsystems

Creating intelligent integrated microsystems, devices that incorporate photonics, electronics, MEMS, and embedded intelligence, presents multiple challenges. The three device technologies have been largely developed independently and have established their own sets of design and process rules that have led to highly stable, high yield processes. In combining these technologies to achieve a desired functionality, constraints are placed on each technology to avoid adverse impacts on the others. Finding a common path towards achieving a single end objective requires process reoptimization and the development of new processes. This paper discusses the dual band adaptive focal plane array (AFPA) that is currently under development, with an emphasis on technology integration and the resulting functional benefits that can be realized. The AFPA device is a dual band IR imaging sensor that enables simultaneous collection of high-resolution MWIR imagery, with spatially independent spectrally tuned imaging in the LWIR for enhanced target detection and classification.

P‐85: Time Dependence of OLED Luminance

The luminance decay of several DC-driven, small-molecule OLEDs has been measured. A simple empirical equation fit the time-dependence for many of the devices. This equation has utility in describing the characteristics of an OLED and may help to identify the causes of the decay.

Motheye Structured Surface Fabrication as Durable Anti-Reflection Treatment on CdZnTe for Space based LWIR Detector Devices

Space based HgCdTe imaging devices, built on CdZnTe substrates, require radiation hardened anti-reflection (AR) treatments in order to withstand the rigors of the space environment. Conventional anti-reflection (AR) coatings provide adequate optical performance but are prone to delamination and degradation due to extreme temperature cycling and irradiation in space. Consequently, there is an intense need for improved AR technology that combines high optical performance with improved durability. Etching physical gradient or motheye structures directly into the CdZnTe eliminates the need to deposit additional layers of different materials onto the substrate, avoiding the possibility of delamination and cross contamination. Motheye AR surfaces, under development at Surmet Corporation, have demonstrated excellent broadband optical performance in the LWIR (7 to14 micron) waveband. Surmets motheye technology involves direct etching of a regular pattern of fine features into the CdZnTe substrate, using standard lithography and dry etching techniques. The results from this ongoing research and development effort are discussed.

Thin film resonators as mass transducers for explosives detection

Sub-miniature thin film resonators (TFR) operating near 2 GHz are being developed as mass transducers for high- sensitivity vapor detection. The TFR sensor are coated with species selective vapor absorbing polymers to develop pattern response to the target species for detection and identification. Eight member arrays of TFR sensor have been fabricated and tested for the detection of characteristics explosive vapors including trinitrotoluene, dinitrotoluene, and dinitrobenzene. The TFR sensor use aluminum nitride as the active piezoelectric element and have ben fabricated with resonator quality factors greater than 200. Response patterns and sensitivity measurements are being made using pure vapors, water solutions of the target species, and solid contaminated with the target vapor species.

Thin film resonators for TNT vapor detection

Progress on the development of a miniature mass transducer for low level vapor detection is described. Thin-film bulk acoustic wave resonators (TFRs) are fabricated with AlN as the piezoelectric layer onto an acoustically reflecting solid substrate. Qs of 200 at 2 GHz have been measured. Comparison of the sensitivity of these 2 GHz TFRs with 250 MHz surface acoustic wave resonators is made. A set of TFRs with species selective coatings has the potential of detecting TNT vapor at the sub PPT level. Detection of 5 ppb TNT with a signal to noise of 200:1 is demonstrated.

Application of physical gradient index (Moth-Eye) structures to ALON windows as a durable anti-reflection treatment

The optical performance of windows and domes are subject to degradation from rain and sand erosion damage in harsh flight environments. While durable window and dome materials, such as ALON®, spinel and sapphire are more or less impervious to rain and sand erosion damage in the captive carry environments, the coatings use to provide antireflection (AR) function are not. Rain and/or sand erosion damage of the outer AR coating leads to degradation of the windows optical performance, even when the underlying window itself is not damaged. Surmet has been working on design and development of physical gradient index (Moth- Eye) structures based AR surfaces etched directly into the surface of the ALON substrate. By eliminating the need for less durable coating materials, these structures offer high optical performance without compromising durability. The difficulty of this approach is that the same durability that makes ALON impervious to erosion damage makes it very difficult to etch. Processes have been developed at Surmet which facilitate the etching of fine deep features into ALON surfaces required for broadband AR function. Recent results will be presented.