A 11×6 element pyroelectric detector array utilizing self-polarized pzt thin films grown by sputtering

A one-dimensional pyroelectric array detector for use as a multielement infrared sensor has been developed by using PbTiO3 bulk ceramics fabricated by a sheet-forming method. This one-dimensional infrared sensor consists of 16 elements. A pyroelectric detector responsivity of 3×104 V/W can be obtained at a 10 Hz chopping frequency, and a specific detectivity D* of 1.2×108 cm·Hz1/2/W has been achieved. The time constant of this pyroelectric detector is about 5.2 ms, so the detector has a shorter response time compared with a commercially available conventional pyroelectric detector. The crosstalk, which influences the output for the adjacent elements, is less than 10%. The output voltage for the detector gradually decreased as the atmospheric temperature increased. Pyroelectric detector responsivity increases with decreasing electrode size. By using this high-performance pyroelectric array detector, the thermal sources at lower temperatures than that of the environment can be detected with high sensitivity, as much as in the case of the thermal sources at higher temperatures.

Pyroelectric infrared detectors have been of interest for many years because of their wide wavelength response, good sensitivity and lack of need for cooling. They have achieved a wide market acceptance for such applications as people sensing, IR spectrometry (especially for environmental protection) and flame/fire protection. Arrays of such detectors, comprising a pyroelectric material interfaced to an application specific integrated circuit for signal amplification and read out, provide an attractive solution to the problem of collecting spatial information on the IR distribution in a scene. Over the past 15 years, this has been particularly explored for uncooled thermal imaging. However, pyroelectric arrays have the property that they are only sensitive to changes in the IR flux. This means that they are particularly-well suited to the monitoring of movements of people in applications such as retail outlets and in safety and healthcare applications. The applications of low cost arrays with limited (few hundred elements) for people sensing and imaging radiometry will be illustrated. The performances and costs of uncooled pyroelectric arrays are ultimately driven by the materials used. For this reason, continuous improvements in materials technology are important. In the area of bulk ceramics, it is possible to obtain significant improvements in both production costs and performance though the use of tape-cast, functionally-gradient materials. The use of directly-deposited ferroelectric thin films on silicon ASIC's is offering considerable potential for low cost high performance pyroelectric arrays. The challenges involved in developing such materials will be discussed, especially from the aspect of low temperature deposition and other fabrication issues, such as patterning. Sol gel deposition provides an excellent technique for thin film growth and will be illustrated with an example of a Mn-doped PZT film that can be grown at 560°C with a FoM FD exceeding that of many bulk materials. The ability to grow such high-performance thin films onto silicon brings with it the ability to fabricate novel MEMS-based pyroelectric device structures. A new concept that will be presented here is the use of arrays of thin film pyroelectric detector elements with integrated radiation collectors designed to greatly enhance the intensity of the radiation falling on the element. The collectors' design is based on the Compound Parabolic Concentrator. These are non-imaging collectors, originally developed for solar cells technology in the 1960's, that yield a concentration ratio near to the thermodynamic maximum. The CPC structure is etched in a silicon wafer, upon which has been defined a pyroelectric IR sensor with low thermal conductance (spiral leg structure) fabricated in a high sensitivity PZT thin film. To our knowledge, this is the first time that CPCs have been applied to microfabricated IR sensors. First experimental assessment of the performance of these structures will be presented. (11 pages)

Gamma-ray irradiation effects on electrical properties of ferroelectric PbTiO3 and Pb(Zr0.52Ti0.48)O3 thin films

Development of people-counting system with human-information sensor using multi-element pyroelectric infrared array detector

Pb(Zr,Ti)O3 (PZT) films with very thin PbTiO3 (PT) buffer layers inserted between the film and the Si/SiO2/Ti/Pt substrate were grown by a rf magnetron sputtering technique. The Xray diffraction patterns and the surface morphology of PT as a function of the thickness, in the range of 20 to 400 Å, were first investigated. Such a marked contrast in morphological features was not observed when the thickness was above 400 Å. The films were grown in-situ at 500°C. We found modification of the PT orientation when its thickness varied between 20 Å and 400 Å. This implies a gradual evolution of the lattice parameters in the nucleation stage of PT films. Insertion of these buffer layers was found to exert marked effects. Up to 400 Å the PT was grown with a [100] preferred orientation. The orientation of PZT could be controlled by changing the thickness and then the orientation of PT. The results will be discussed in terms of the effects of the buffer layer on the crystalline structure and the surface morphology of PZ

Combined theoretical and nanoscale experimental study of Pb(Ca,Ba)TiO3, Pb(Sr,Ba)TiO3, and Pb(Sr,Ca)TiO3 complex perovskite structures: An investigation of the ferroelectric and electronic properties

Piezoelectric films using sol-gel composites could be useful as ultrasonic transducers in various industrial fields. For sol-gel composite film fabrication, the spray coating technique has been used often because of its adaptability for various substrates. However, the spray technique requires multiple spray coating processes and heating processes and this is an issue of concern, especially for on-site fabrication in controlled areas. Stencil printing has been developed to solve this issue because this method can be used to fabricate thick sol-gel composite films with one coating process. In this study, PbTiO3 (PT)/Pb(Zr,Ti)O3 (PZT) films, PZT/PZT films, and Bi4Ti3O12 (BiT)/PZT films were fabricated by stencil printing, and PT/ PZT films were also fabricated using the spray technique. After fabrication, a thermal cycle test was performed for the samples to compare their ultrasonic performance. The sensitivity and signal-to-noise-ratio (SNR) of the ultrasonic response of PT/PZT fabricated by stencil printing were equivalent to those of PT/PZT fabricated by the spray technique, and better than those of other samples between room temperature and 300°C. Therefore, PT/PZT films fabricated by stencil printing could be a good candidate for nondestructive testing (NDT) ultrasonic transducers from room temperature to 300°C.

Nanograined PbTiO3 (PT) thick films were deposited on Si, yttria‐stabilized zirconia (YSZ), and Ni substrates using an aerosol deposition (AD) method at room temperature. The AD PT thick films on each different substrate were annealed at 500°C and 700°C for 1 h to increase the crystallinity. The stresses in the PT film were modulated by controlling the difference in the coefficient of thermal expansion (CTE) between the films and substrates during the thermal annealing process. The morphology of the AD PT films was examined from the polycrystalline dense structure (thickness ~8 μm), and the changes in the crystallographic phase, in‐plane stresses, and ferroelectric properties in annealed films were investigated. In‐plane stress analysis showed that the PT films annealed at 500°C and 700°C on each substrate exhibited compressive stress. Owing to the effects of compressive stress in the PT film, the film showed less tetragonality (c/a ratio) and enhanced ferroelectric behaviors. The change in the polarization–electric field (P–E) hysteresis loop of the PT films was explained by the stress induced from CTE mismatch between the films and substrates.

Sol-gel-derived Pb(Zr, Ti)O3 films with thin, room temperature sputter-deposited and postannealed Pt/La0.5Sr0.5Co1.0O3 top and La0.5Sr0.5Co1.0O3/SrTiO3/Pt/SrTiO3 bottom electrodes were synthesized on SiO2/Si(100) substrates, and the microstructures and ferroelectric properties were examined. Insertion of SrTiO3 layers with optimum thicknesses in the bottom electrode improved surface roughness of the bottom electrode and the Pb(Zr, Ti)O3 film, and strengthened the adhesion of the bottom electrode to the substrate. The stacking of La0.5Sr0.5Co1.0O3, SrTiO3 and Pt layers in the bottom electrode yielded Pb(Zr, Ti)O3 (40/60) films with flat surfaces; the fatigue tests at 3 V, 100 kH indicated that switchable polarization was greater than 15 µC/cm2, and no fatigue degradation was observed up to 1010 cycles. However, the PZT films with higher Ti concentration in the composition exhibited gradual decay in polariation from fatigue cycles of 106. The possible reason for the decay in polarization was discussed. The leakage current was of the order of 10-5 A/cm2 at driving voltages of 2–3 V; considerable scattering among the leakage current data was observed.

Single c–domain single crystal PbTiO3 (PT) thin films were prepared by sputtering on both miscut (001)SrTiO3 (ST) and (110)SrRuO3/miscut (001)ST substrates with a miscut angle of 1.7°. Film thickness ranged from 5 nm to 250 nm. The film growth was governed by step-flow growth and the film surface was atomically flat. The lattice misfit strain induced during the film growth was quenched. The PT films were tetragonally deformed and tightly bonded to the ST. The PT films showed no anomaly on the curves of lattice parameter in terms of temperature (temperature range, room temp. to 600°C), due to their excellent interfacial quality, although anomalies are expected at the Curie temperature (around 490°C in bulk PT). The P/E loops suggest that the saturation polarization Ps was 40 μC/cm2 with a high coercive field of 400 to 500 kV/cm and a dielectric constant of 60 to 70 at 1 KHz. The Ps of the PT thin film is about half that of bulk PT.

The direct piezoelectric properties of sol–gel-derived Pb(Zr,Ti)O3 (PZT) films in the longitudinal (31) and transverse (33) modes were investigated to determine the applicability of the film to a piezoelectric vibration energy harvester. For the 31-mode characterization, PZT films were deposited on Pt/Ti/SiO2/Si substrates. The direct piezoelectric properties were characterized by the substrate bending method. The e31f coefficient of the 3-µm-thick PZT film with morphotropic phase boundary (MPB) composition was calculated to be -9.1 C/m2 at a strain of 6×10-5. For the configuration of 33-mode measurement, the PZT films were deposited on SrTiO3(STO) substrates without bottom electrodes and characterized in the same manner. In this configuration, the 3-µm-thick (100) PZT film with MPB composition has a larger piezoelectric response than (111) PZT films. The e33* coefficient of the (100) PZT film was measured to be 5.4 C/m2. When the PZT film thickness decreased to 1 µm, the coefficient increased to 7.7 C/m2, suggesting that the non polarized region existed near the STO substrate owing to the lateral poling configuration.

The microstructures and electrical properties of thin and thick Pb(Zr0.52, Ti0.48)O3 (52/48 PZT) films for microdevice applications with thicknesses from 480 nm to 2.3 µm on 350 nm Pt(111)/40 nm Ti/300 nm SiO2/Si 525 µm substrates fabricated by a sol–gel multicoating process were investigated. These PZT films showed dense and homogeneous surface microstructures. The crystalline structures of 480-nm-thick PZT films showed a (111) preferred orientation over (100), (200) and (110) orientations. The intensity ratios of (100) and (200) to (111) increased at PZT film thicknesses greater than 480 nm. By Auger electron spectroscopy, small-composition-variation peaks at an interval of approximately 120 nm at interfaces produced by each PZT coating process of 480 nm PZT films were found. Dielectric constants increased from 825 to 880 at 100 kHz and PZT film thicknesses from 480 nm to 2.3 µm. The Pr and Ec of 2.3-µm-thick PZT films were about 30 µC/cm2 and 58 kV/cm, respectively. The e31,f of 1-µm- and 2-µm-thick PZT films was characterized by the fabricated e31,f measurement system before and after poling.

The use of surface-micromachining techniques combined with standard VLSI techniques to fabricate a 64-element*64-element imager for infrared heat detection is described. A large array of pyroelectric detectors (ZnO/PbTiO/sub 3/) was vertically integrated on top of the integrated circuitry. The operation and fabrication of the circuit are described. Device and circuit characterization, carried out prior to and after microsensor processing, showed no significant degradation. The chip area per sensor is significantly reduced by use of surface micromachining rather than bulk machining methods. The ability to fabricate these microsensors in VLSI NMOS and CMOS processes suggests further integration of ZnO-based sensors with high-density standard cell analog and digital building blocks. >

Pb(Zr,Ti)O3 (PZT) thin films have attracted great attention due to their superior ferroelectric, pyroelectric and piezoelectric properties. The epitaxial films on single-crystal substrates are expected to possess enhanced properties compared with polycrystalline films on conventional silicon wafers. We prepared epitaxial PZT films on STO (STO) substrates with different orientation by using a sol-gel method. The preparation parameters were optimized to improve crystallization of the films. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PZT film was formed on the {100} surface of the STO substrate, whereas [111]-oriented rhombohedral PZT film on the {111} surface.

In-plane orientation-controlled Pb(Zrx,Ti1−x)O3 (PZT) films with a thickness of approximately 2 µm and a Zr/(Zr + Ti) ratio of 0.39–0.65 were grown on (100) Si substrates by pulsed metal–organic chemical vapor deposition (MOCVD). In-plane-oriented epitaxial PZT films and in-plane random fiber-textured PZT films with {100} out-of-plane orientation were grown on (100)c SrRuO3//(100)c LaNiO3//(100) CeO2//(100) YSZ//(100) Si and (100)c SrRuO3/(100)c LaNiO3/(111) Pt/TiO2/SiO2/(100) Si substrates, respectively. The effects of Zr/(Zr + Ti) ratio and in-plane orientation on the crystal structure, dielectric, ferroelectric, and piezoelectric properties of the films were systematically investigated. The X-ray diffraction measurement showed that the epitaxial PZT films had a higher volume fraction of (100) orientation than the fiber-textured PZT films in the tetragonal Zr/(Zr + Ti) ratio region. A large difference was not detected between the epitaxial films and the fiber-textured films for Zr/(Zr + Ti) ratio dependence of the dielectric constant, and remanent polarization. However, in the rhombohedral phase region [Zr/(Zr + Ti) = 0.65], coercive field was found to be 1.5-fold different between the epitaxial and fiber-textured PZT films. The maximum field-induced strains measured at 0–100 kV/cm by scanning atomic force microscopy were obtained at approximately Zr/(Zr + Ti) = 0.50 and were about 0.5 and 0.3% for the epitaxial and fiber-textured PZT films, respectively.