Ferroelectric Technology Research Articles

Ferroelectric memory: on the brink of breaking through

With a memory-cell size comparable to that of a DRAM memory cell and a manufacturing process similar to that of a stacked high-density DRAM, it can be expected that the ferroelectric technology will leverage off DRAMs and leap frog to higher memory densities. Cost analysis projects cost competitiveness with flash memory and EEPROM. Ferroelectric memory technology has been shown to have reliability levels comparable to or better than other reprogrammable nonvolatile semiconductor memories. High levels of radiation hardness make these memories suitable for near and deep-space applications. Many large semiconductor companies have substantial efforts to develop and introduce ferroelectric memories into the market.

New phase shifters and phased antenna array designs based on ferroelectric materials and CTS technologies

As the search continues for low-cost and high-performance components for the front-end devices for wireless communications systems, some focus has been placed on exploring new and innovative designs based on ferroelectric technology. In this paper, we present new phase-shifter designs and an integrated phased-array antenna system based on the use of multilayer ferroelectric materials and the continuous transverse stub (CTS) technologies. Simulation results show that with the appropriate selection of the materials properties and the dimensions of the multilayer dielectric system, insertion losses may be reduced by as much as a factor of 100. These results also show that while only a slight reduction (15%) in the maximum achievable tunability was observed, it was possible to achieve significant improvement in impedance-matching characteristics. A procedure to enhance the radiation efficiency from an integrated ferroelectric/CTS phased antenna array design is described and specific array designs are discussed.

Round table discussion, FWPR'99: Future trends in ferroelectric research and technology

The round table discussion capped off two days of very interesting talks, and intense discussions in the general area of ferroelectric and dielectric materials. The RTD focused on the “Future of Ferroelectric and Dielectric Thin Film based Technologies.” The panelists, with active participation from the audience (including the moderator), discussed several aspects of this important area. The overall conclusion was that Ferroelectric Thin Film based technologies are in a very active phase of development. There are immense opportunities in this field for research, development, and productization. In parallel, there was concern about the sustainability of research and development activities, especially in the US, given the sparse federal funding in this area. The discussion was broadly categorized into: (i) Applied and Market Issues and (ii) Fundamental Issues. The discussion generally went along technology lines, with considerable discussion on memories, microwave components and markets.

Potential impact of ferroelectric technology for PCS and cellular communications

As the cellular and PCS spectrum become increasingly crowded due to the presence of a greater number of subscribers, it will become even more important for handset and base station manufacturers to come up with ways to ensure reliable system performance. In the handsets, the use of tunable filters, along with lower phase noise tunable oscillators, among other things, can help achieve the desired increase in reliability and system performance. It is in these areas where frequency agile components may be best applied. Ferroelectric thin/thick film technology is making significant improvements in reducing dielectric loss and tuning voltage requirements. Thus their application to the development of commercially useful and practical frequency agile components is gaining. This paper will consider some of the potential areas in filtering and tunable oscillator design where ferroelectric materials may be used to an advantage in future generation handsets.

Orientation controlling of PZT thin films derived from sol-gel techniques

The factors that influence the crystal orientation of lead zirconate titanate (PZT) thin films fabricated by using sol-gel techniques on (111) preferred oriented Pt/Ti/SiO2./Si(100) substrates were systematically investigated. The crystallization treatment of PZT thin films was done at 650 ◦C for 30 min by using rapid thermal annealing (RTA). X-ray diffraction (XRD) analysis was used to identify the orientation of PZT thin films. The morphology was examined by using scanning electron microscopy (SEM). The different ratio of zirconium to titanium, the lead contents in precursor solutions, the modification of the PZT precursor and the thickness of PZT thin films have obviously effects on the formation of (111) or (100) preferred-oriented and random-oriented PZT thin films. It is concluded that controlling the orientation of PZT thin films can be realized by using the sophisticated sol-gel processing and normal (111) Pt/Ti/SiO2./Si(100) substrates. Electrical properties of ferroelectric thin films are strongly dependent on their crystallographic orientation, which determines the magnitude of switchable polarization of a thin film. Among the applications for which highly oriented PZT thin films will be of interest are pyroelectric detectors, optical disk storage system, optical waveguide devices, and spatial light modulators. A further benefit of orientation may be enhancing process integration of ferroelectric thin film and semiconductor technologies. Many studies for the control of a preferred orientation in PZT films are usually based on the substrate used. Most of them use various single crystals as substrates to fabricate the crystal alignment of the PZT thin films. For example, PZT films with (100), (110), and (111) textures can be obtained by using single-crystal SrTiO3 or MgO wafers of the same orientation [1]. But single-crystal substrates have economical problem for applications of the ferroelectric thin films. It is necessary to develop a method for the control of the PZT orientation using relatively cheaper substrates. RF magnetron sputtering [2], metal organic chemical vapor deposition (MOCVD) [3], and pulsed laser deposition (PLD) [4] methods have been widely utilized to produce highly oriented or epitaxial ferroelectric thin films. Chemical process has the advantages of feasible

Evaluation of Ferroelectric BaxSr1−xTiO3 Thin Films Driven by Phase Shifters for Reflectarray Applications

ABSTRACTThe application of ferroelectric thin films for the development of frequency and phase agile microwave components has been the reason behind very encouraging demonstrations of tunable microwave devices in recent years. Thus, one could conclude with basically a general consensus, that the question of the suitability of thin film ferroelectric technology for the fabrication of superior tunable microwave components has been already answered in a favorable way. However, what is still pending in regards to the validation of this technology is the development of evaluation methodologies to set forth the standards for the material quality and subsequent performance criteria of specific components and devices based on this technology. In this paper we discuss the evaluation methodology under implementation at NASA Glenn Research Center aimed at identifying and optimizing the most relevant parameters of BaxSr1−xTiO3 (BSTO) ferroelectric thin films (i.e., tunability, losses, thickness, crystalline quality, etc.) as defined by a specific microwave application (in our case, phase shifters for reflectarray antennas). Results of our material analysis based on X-ray diffraction and ellipsometry, and how these properties correlate with RF performance for a targeted circuit, will be presented.

Single event upset immunity of strontium bismuth tantalate ferroelectric memories

An embedded 1 Kbit nonvolatile (NV) serial memory manufactured with strontium bismuth tantalate (SBT) ferroelectric (FE) technology was shown to be immune to effects of heavy ion irradiation. The memories did not lose any data in the non-volatile mode when exposed to xenon (maximum effective LET of 128 MeV-cm/sup 2//mg and a total fluence of 1.5/spl times/10/sup 7/ ions/cm/sup 2/). The ferroelectric memories also did not exhibit any loss in the ability to rewrite new data into the memory bits, indicating that no significant degradation of the FE dipoles occurred as a result of the heavy ion exposure. The fast read/write times of FE memories also means that single event gate rupture is unlikely to occur in this technology.

Piezoelectric bimorph cantilever for actuating and sensing applications

Back side bulk micromachining has been combined with front side ferroelectric technology for making a piezo-active microsystem including a sensor and an actuator on a silicon cantilever. Stress and thickness control of the thin (10μ) silicon beam are obtained by an original technology. The PZT piezoelectric material is deposited by the sol-gel spin coating technique. Due to the partial incompatibility of piezoelectric PZT capacitor with the methods of IC processing, a new processing route had to he found that is able to protect the sensitive area on the front side during back side micromachining. Additionally, a new method to pattern aluminum metallization in contact with platinum had to he developed to avoid electrochemical reactions in etching solutions The beam can he sensed and actuated by the piezoelectric direct and (resp) converse effects, Sensor voltage response and actuator displacement are given up to the resonance frequency of 2.6 kHz. The device is planned to he used in a self regulated closed loop where the feedback electronics will be integrated on the chip.

Performance comparison of ferroelectric liquid-crystal-technology-based coherent optical multichannel correlators

Our purpose is to compare two architectures when implemented with ferroelectric liquid-crystal technology: the conventional VanderLugt and joint transform correlators. The architectures are compared in the single-correlation and multichannel cases. The analysis covers both theoretical aspects and practical considerations regarding implementation. Specifications for a multichannel correlator design, including considerations of both spatial light modulators and architecture configurations, are discussed. Experimental results are presented for both architectures. Finally, the benefit resulting from extension to multichannel operation is discussed in terms of both multiplexing and algorithmic capabilities.

Plasma etch processing of advanced ferroelectric devices

Ferroelectric structures are being used in SRAM devices and are migrating to DRAM devices. A DRAM cell size can be dramatically reduced by employing ferroelectric structures in place of the current silicon oxide capacitor structures. A 5μ2 DRAM cell capacitor can be reduced in size by a factor of 20 using a ferroelectric structure. The current technology used to etch ferroelectric device layers has at least two major shortcomings. The first etch issue is the sloped profiles (i.e. 40°) which are a result of the high ion energies used to etch the relatively non volatile materials (Platinum and PZT). The second etch issue is severe sidewall redeposition when vertical profiles are obtained by using ion mills etc. The etch products that are redeposited on the sidewalls become very difficult or impossible to remove in a manufacturing environment. Profiles of > 75° without heavy redeposition will be required in order for 0.5μ DRAMs to be produced using ferroelectric technology. A series of designed experiments were developed to understand the dependent variables impact on reducing residues and increasing the etched feature's profile angle. Response surfaces were developed for resist selectivity, profile angle, and etch rate versus changes in KHz power, cathode temperature, reactant gas flow and additive gas flow in an HRe − (High Density Reflected Electron) etch system. The process results (optical emission and SEM analysis) were statistically evaluated and process trends developed. The resulting response surface graphs combined with SEM micrographs demonstrate trends in profile control and etch rate. The process trends are reviewed which result in > 75° residue-free etching of ferroelectric devices.

Integration technology of ferroelectrics and the performance of the integrated ferroelectrics

Abstract We have successfully incorporated the ferroelectric and the high dielectric constant capacitors into integrated circuits. The GaAs MMICs with BST capacitors have been widely used for cellular phones. The BST technology is also applied to a silicon CCD delayline processor for VCRs and camcorders. With respect to the ferroelectric technology with Y1, an experimentally fabricated 256k bit FeRAM has exhibited the remarkable performance of the 100 ns and 3V operation with a 1T/1C cell configuration dedicated for the FeRAM. These integrated ferroelectrics have been achieved by controlling the ferroelectric properties in thin films and incorporating the films into GaAs and silicon devices with outstanding process technology. Furthermore, we refer to the memory cell design technology which enables the FeRAM to work below 1V. Various advantages of low-voltage and high-speed operation inherent in integrated ferroelectrics will be emphasized on the intelligent microelectronics applications toward the next multimedia generation.

PVDF ultrasonic sensors for location of small objects

Abstract Ultrasonic proximity sensors are, in general, too bulky to be placed directly on robotic end-effectors, such as grippers or anthropomorphic hands, which are also equipped with force-torque or tactile sensors and include part of the electronic unit. For this reason there is a pressing need to reduce the size and weight of any kind of sensory system mounted on robotic end-effectors and many efforts are being directed toward this aim. In the field of ultrasonic sensors, since the strong damping introduced by air imposes work at low frequency (not higher than a few hundred kHz), restricted choices of materials and transducer shape and dimension are necessary. This work presents an ultrasonic sensor for robotic grasping systems and short-range application, based on ferroelectric polymer technology, which is very light, small and cost-effective. The sensor, quite similar in configuration to what has already been considered elsewhere, consists of two unimodal transducers realized by curving a strip of 24 μm thick PVDF in a hemicylindrical configuration. The ultrasonic sensor has a theoretical resonance frequency of about 175 kHz and operates in a short range of 200 mm, although lower-frequency transducers can be used up to 400 mm. Details on the transducer design and characterization will be given and its application for the location of randomly oriented objects a few milimetres in size will be discussed. Finally, the calculation of the tilt of both flat and rough surfaces between 0 and 30° is considered.

A ferroelectric material development test chip

The approach taken in the development of this Ferroelectric Material Test Chip (FMTC-3861) was to design test structures which allow for the extraction and evaluation of critical process and device parameters, as well as making a judgement concerning the relative magnitude of their effects on overall ferroelectric device performance. This paper discusses the design of the FMTC-3951 developed by Harris to evaluate the performance level of a three micron ferroelectric capacitor technology. Numerous electrical and parametric test structures are contained in FMTC-3861, including: various process monitoring, defect density, and ferroelectric capacitor test structures. Ferroelectric thin film electrical and material characteristics such as polarization, fatigue, aging, switching, TDDB, DC breakdown, leakage, etc. can be studied as a function of material deposition methodology and crystalline stoichiometry, capacitor area, capacitor layout orientation, capacitor geometric shape, electrode type and configuration,...