Glen Fox

Properties of reactively sputtered IrOx for PZT electrode applications

Abstract The use of IrOx for electrodes in PbZrxTi1−xO3 (PZT) capacitors for ferroelectric memory applications has proven to be advantageous in several respects. In comparison with Pt, IrOx often exhibits improved fatigue and provides resistance to hydrogen induced degradation at elevated temperatures. Since IrOx is often produced by sputtering in an oxygen containing environment, several forms of IrOx can be produced depending on the process conditions. This work concentrates on an analysis of the DC reactive sputtering of IrOx from an Ir metal target. As with other oxidizable metals, Ir exhibits a transition between metal and oxide mode sputtering when sputtered in oxygen containing atmospheres. Variations in the Ar/O2 gas flow ratio were used to produce Ir and IrOxfilms on both sides of the metal-to-oxide mode reactive sputtering transition. Changes in the IrOx film properties were quantified by using a combination of metrics including X-ray diffraction, sheet resistance, and stress. It was found that the, IrOx crystalline structure and other IrOx properties could be directly related to the ferroelectric switching performance of PZT capacitors with IrOxtop electrodes. A relationship between IrOx deposition processes and resistance to etch induced damage of the ferroelectric properties was also observed.

High endurance scaled plzt thin films for fram applications

Abstract Lower operating voltage is one of the main requirements of future generation FRAM. In order to achieve this requirement, PLZT thin film capacitors must be scaled down with respect to thickness. This paper presents the ferroelectric performance of scaled PLZT thin films. The thickness of RF magnetron sputtered PLZT thin films was scaled down to 1000Å. Integrated array capacitors (measured after local interconnect formation) using the scaled 1000Å PLZT thin films showed good switching performance, excellent endurance (fatigue free up to 1012 fatigue cycles) and good data retention. An approach to accelerate the fatigue process using high electric field is introduced in order to shorten the endurance testing time at extended fatigue cycles such as above 1011 cycles. The thickness scaled PLZT thin films, showing dramatically improved ferroelectric performance, can be applied to the manufacturing of low voltage FRAM products.

Progress in economically viable phase shifters based on thin ferroelectric films

Abstract A considerable amount of work has been done in the area of frequency and phase agile microwave circuits employing thin ferroelectric films. The best films to date have been BaxSr1-xTiO3 (BST) grown by pulsed laser ablation. But laser ablation does not seem readily scalable for volume manufacturing, partly because the process appears limited to 5 cm diameter wafers or smaller. Another impediment to commercialization is testing. Testing is cumbersome because the devices must be inserted into a fixture to interface with coaxial launchers. And, high voltage bias tees are not commercially available to safeguard the microwave instrumentation. We have investigated alternate growth methods including MOCLD, CCVD, and sputtering and developed an on-wafer testing approach for screening phase shifters. Some of the results are reported in a companion paper. Here we report results for sputtered PLZT films on LaA1O3. Coupled microstrip phase shifters at K-band produced a figure of merit of ≈29°/dB. This is within a factor of two of the best laser ablated BST films. The devices also had an uncharacteristically flat frequency response between 12 and 20 GHz. Considering the large lattice mismatch between LaA1O3 and PLZT, the film crystallinity is very good as determined by XRD. Surprisingly, the films also appeared to be cubic. We also report results for CCVD Ba0.57Sr0.43TiO3 on sapphire. 20 GHz phase shifters yielded a figure-of-merit of 18°/dB. Finally we report the design and performance of a coplanar-to-microstrip transition that permits the phase shifters to be tested on wafer. Devices that pass have the virtual ground probe pads diced off so the phase shifter can be integrated into a phased array. Bias is fed directly through the coplanar probes and isolated from the network analyzer by custom high voltage bias tees.

X-Ray Diffraction Method for Determining Textured Volume Fractions in PZT Thin Films

The crystallographic texture of PZT thin films has been proven to play a critical role in the electrical performance of PZT used in non-volatile FRAM. During both development and production of FRAM, PZT texture must be monitored to assure ferroelectric performance. A common method for monitoring texture is to use normalized intensities collected from X-ray diffraction 2-theta scans. Although this method can reveal thin film texture, it does not give a quantitative measure of the volume of textured and/or random material. In addition, this method can only be used to compare films with constant thickness since differences in X-ray absorption are not taken into account. A new method for calculating the volume fractions of textured and randomly oriented material in PZT thin films has been developed. This new method for calculating textured volume fractions still utilizes integrated intensities from 2-theta scans, but the calculations include corrections for film thickness and geometrical factors. The calculated volume fractions obtained from this new method of data analysis can be used directly for physical evaluation of PZT thin film ferroelectric performance.

Relationship between PB content, crystallographic texture and ferroelectric properties of plzt thin films for FRAM® applications

Abstract In order to have better control of ferroelectric properties and fast PLZT thin film quality control monitoring during FRAM processing, a correlation between ferroelectric performance, Pb content and crystallographic texture needs to be established for RF magnetron sputtered PLZT thin films. The ferroelectric performance of 200 nm PLZT thin films that contain different levels of Pb excess and different volume fractions of {100} textured materials were investigated. It was found that a higher Pb excess in the as-sputtered PLZT film leads to a higher volume fraction of {100} textured crystallites after annealing. Highly {111} textured PZT thin films show a relatively high Qsw (≈2Pr), however the fatigue and the aging performance is not optimized. The optimized range for the volume fraction of {100} textured material was identified. PLZT thin films, of which the {100} volume fraction is in die optimized range, exhibit improved fatigue and aging performance, better suited for FRAM application.

SBTN thin film capacitors prepared by RF-magnetron sputtering

Abstract Thin films of Bi based layered-structure solid solution, SrBi2Ta2O9-SrBi2Nb2O9 (SBTN), were prepared by conventional single target RF-magnetron sputtering on Pt/Ti/SiO2/Si substrates with a diameter of 6 inches. The capacitors were fabricated by patterning the top Pt electrode using photolithography. SBTN thin films with random and c-axis preferred orientation were obtained using RTP annealing and conventional furnace annealing, respectively. The electrical properties were characterized by both the hysteresis and pulsed field methods. A 2Pr of 24 μC/cm2 and Ec of 125kV/cm were measured from randomly oriented 1600A films. The films exhibit excellent fatigue performance.

Comparison of CSD and sputtered PZT with iridium electrodes

Abstract Several recent reports have combined Ir electrodes with PbZrxTi1−xO3 (PZT) made by chemical solution deposition (CSD) to produce capacitors with low fatigue rates, but the same behavior has not been reported for sputtered PZT with Ir electrodes. This paper presents a comparison of the performance of sputtered and CSD PZT capacitors with Ir electrodes. It was found that replacing the Pt top electrode with Ir was sufficient for obtaining improved fatigue performance for both sputtered and CSD deposited PZT. A comparison of Ir and Pt top electrodes shows that Ir can extend the number of useful switching cycles by 3 to 4 orders of magnitude for both sputtered and CSD deposited PZT. As has been previously observed for Pt electrodes, the fatigue with Ir top electrodes is dependent on the switching voltage. Excellent fatigue performance has been observed to 1011 cycles for both 3 and 5 V switching potentials. In addition to fatigue performance, a detailed analysis of switching, retention and leakage cur...

Comparison of sputtered SBTN and PLZT thin film capacitors for FRAM applications

Abstract Thin films of the solid solution SrBi2Ta2O9-SrBi2Nb2O9 (SBTN) and Ca and Sr doped (Pb, La)(Zr, Ti)O3 (PLZT) were prepared by conventional, single target, rf-magnetron sputtering. The films were deposited onto Pt coated substrates with a diameter of 6 inches. The electrical properties were characterized by hysteresis and pulsed field switching measurements. A ferroelectric performance comparison between two types of capacitors will be presented. The recent improvement in PLZT capacitor processing have greatly extended fatigue resistance beyond what is usually observed and reported for SBTN capacitors.