Howard R. Beratan

Uncooled monolithic ferroelectric IRFPA technology

Once relegated to expensive military platforms, occasionally to civilian platforms, and envisioned for individual soldiers, uncooled thermal imaging affords cost-effective solutions for police cars, commercial surveillance, driving aids, and a variety of other industrial and consumer applications. System prices are continuing to drop, and swelling production volume will soon drive prices substantially lower. The impetus for further development is to improve performance. Hybrid barium strontium titanate (BST) detectors currently in production are relatively inexpensive, but have limited potential for improved performance. The MTF at high frequencies is limited by thermal conduction through the optical coating. Microbolometer arrays in development at Raytheon have recently demonstrated performance superior to hybrid detectors. However, microbolometer technology lacks a mature, low-cost system technology and an abundance of upgradable, deployable system implementations. Thin-film ferroelectric (TFFE) detectors have all the performance potential of microbolometers. They are also compatible with numerous fielded and planned system implementations. Like the resistive microbolometer, the TFFE detector is monolithic; i.e., the detector material is deposited directly on the readout IC rather than being bump bonded to it. Imaging arrays of 240 X 320 pixels have been produced, demonstrating the feasibility of the technology.

Advances in monolithic ferroelectric uncooled IRFPA technology

The success of uncooled IR imaging at Raytheon has awakened a new view of the potential of thermal imaging. Once relegated to only expensive military platforms, occasionally to civilian platforms, and envisioned for individual soldiers, thermal imaging is now affordable for police cars, commercial surveillance, driving aids, and a variety of other industrial and consumer applications. System prices are as low as

Thin film ferroelectrics: breakthrough

8000, and swelling production volume will soon drive prices substantially lower. The impetus for further development is performance. The hybrid barium strontium titanate (BST) detectors currently in production have limited potential for improved sensitivity, and their MTF is suppressed at high frequencies. Microbolometer arrays in development at Raytheon have demonstrated performance superior to hybrid detectors. However, microbolometer technology lacks a mature, low-cost system technology and an abundance of deployable system implementations. Thin-film ferroelectric (TFFE) detectors have all the performance potential of microbolometers, and arguably more. They are also compatible with numerous fielded and planned system implementations. Like a microbolometer, the TFFE detector is monolithic; i.e., the detector material is deposited directly on the readout IC rather than being bump bonded to it. Initial imaging arrays of 240 X 320 pixels have been produced, demonstrating the feasibility of the technology.

Low Temperature PZT Film by MOCVD

Now that commercial infrared is a well-established business with several serious competitors, the pressures for a competitive edge have increased dramatically. Hybrid barium strontium titanate (BST) ferroelectric detectors still provide the basis for the majority of systems being produced today, and tens of thousands of systems have been fielded. The system simplicity of these AC-coupled systems is not matchable by any other current technology, but the complexity of the detector fabrication process limits its potential for further substantial cost and performance improvements. DC-coupled VOx bolometers, currently the most popular technology among manufacturers, offer better sensitivity at somewhat greater cost. Although this technology has been heralded as the technology of the future, it is encumbered by a more complicated system architecture and by spatial noise, which limits the ability to take advantage of its greater sensitivity. Thin-film ferroelectric (TFFE) detectors promise to remove the cost and performance barriers that lie ahead of BST technology, while maintaining the low system cost and low spatial noise characteristic of AC-coupled systems. Until recently the promise has been elusive, but now real-world performance of the best of TFFE systems is competitive with the best of any other technology.

Uncooled infrared detectors and focal plane arrays

Lead Zirconium Titanium Oxide (PZT) thin films were prepared at low temperature using a SMI Metal Organic Chemical Vapor Deposition SpinCVD™ tool. Films prepared by this technique were evaluated for multiple device applications. The low temperature PZT film process addresses problems with device manufacture encountered by techniques that rely on high thermal budgets to obtain superior materials properties. Film growth processes were developed based on the following criteria: low defect density, a high necked and dense microstructure, and highly uniform properties across the wafer. The growth process, ferroelectric film properties, and suitability for IR sensing and FRAM applications are discussed.

Enhanced Infrared Absorption by Ferroelectric-Conducting Oxide Thin-Film Structures

Over the past several years, uncooled IR detectors and focal plane arrays have been rapidly developed. Impressive progress has been made in both resistive microbolometers and pyroelectric thin-film detectors with noise equivalent temperature differences projected to be 10 to 20 mK with F/1 optics for such structures. Noise equivalent temperature of 50 mK bulk pyroelectric detectors and thin film resistive microbolometers are already demonstrated and in production. Other novel schemes, such as bimaterial capacitors, are also promising for uncooled IR detection. The US Army Research Laboratory is involved in developing ferroelectric materials to take advantage of the pyroelectric properties. The goal is to develop crystal oriented thin films to further improve detector performance. In this presentation, the operating principle of resistive microbolometers and pyroelectric detectors, and recent progress of uncooled RI focal plane arrays are discussed. In addition, the uncooled RI detector program at the Army Research Laboratory, that includes research facilities for and research efforts toward uncooled detectors and focal plane arrays is presented.

Systematic investigation of the growth of LaNiO3/PZT/LaNiO3/Si and LaNiO3/PZT/LaNiO3/polymer/Si for IR detector applications

Infrared absorbing free-standing bridge structures are anticipated to be used in the next generation of ferroelectric uncooled infrared detectors. These structures will consist of resonant cavities with an absorbing bridge element, which contains the ferroelectric detector and the contact electrodes. An oxide electrode is preferable to a metallic electrode, because the metallic electrode reflects too much of the incoming radiation at reasonable thickness. For this paper, spectral transmission and reflection of lanthanum nickelate (LNO), barium ruthenate (BRO) and strontium ruthenate (SRO) films were measured, and it was found that the properties could be described as a simple two-dimensional conducting sheet. The optical absorption of several free-standing bridge structures was modeled, and optimized dimensions and electrode conductivity are presented which yield greater than 80% absorption over the full 8-14 w m band.

THERMAL DETECTOR AND METHOD OF MAKING THE SAME

We have been focused on growth of multi-layered LaNiO3/Pb(Zr,Ti)O3/LaNiO3 on bare Si and polymer-coated Si substrates for infrared detector applications. A unique ion-beam assisted pulsed laser deposition (IBAD-PLD) has been employed to address two critical issues related to these thin film ferroelectric (TFFE) devices: to reduce the thermal budget and to enhance the texture of the devices. IBAD has been a well-known technique for deposition of thin films due to the ability to control morphology, adhesion, texture, and stoichiometry of the film by providing extra kinetic energies to, and to generate desired textures in films by preferential sputtering of the growing surface of the film. We have studied the role of several processing parameters of IBAD-PLD process, including ion-beam energy, current density, IBAD time, and substrate temperature in order to identify the best processing window for LaNiO3/Pb(Zr,Ti)O3/LaNiO3.