PZT Capacitors Research Articles

Highly transparent PZT capacitors on glass obtained by layer transfer process

Transparent ITO/PZT/ITO capacitors were fabricated on 200 mm glass substrate. The PZT films of 1 µm and 2 µm thickness were first grown on platinized Si wafer by sol–gel method, and then transferred onto glass substrate together with ITO electrodes following an innovative process. The obtained PZT based stacks on glass show an average transmission of about 70% in the visible range. PZT films keep their preferred (100) orientation after transfer process. The capacitors exhibit ferroelectric, dielectric and piezoelectric properties comparable to standard non-transparent PZT films with metal electrodes. Transverse piezoelectric coefficient e31,f as high as 16 C/m2 was measured for both PZT film thicknesses. This proof of concept opens the way to the fabrication of transparent piezoelectric actuators on glass for high performances haptic devices, as well as for other emerging applications like self-cleaning or functionalization of smart windows.

Enhanced Ferroelectric and Piezoelectric Properties in Graphene-Electroded Pb(Zr,Ti)O3 Thin Films.

While using ferroelectric polarization to tune the functional properties of 2D materials has been extensively studied recently, the effects of 2D materials on the ferroelectricity and piezoelectricity of ferroelectrics are much less explored. In this work, we report markedly enhanced ferroelectric and piezoelectric properties of graphene/Pb(Zr0.52Ti0.48)O3/SrRuO3 (GR/PZT/SRO) capacitors. Compared with conventional metal-electroded ferroelectric capacitors, the GR/PZT/SRO capacitors exhibit more abrupt polarization switching, larger switchable polarization, lower leakage current, and smaller coercive voltage. Moreover, with graphene electrodes, the ferroelectric properties of PZT capacitors are much more stable against aging. The enhanced ferroelectric behaviors in GR/PZT/SRO capacitors can be attributed to an improved interface with fewer defects and inhibited growth of defective interfacial layer resulting from the graphene protection. Because of the atomic thickness and extraordinary mechanical flexibility of graphene, the piezoelectric response in PZT with graphene electrode is about four times larger than the one with an Au electrode. Our findings on the enhanced ferroelectric and piezoelectric properties of PZT with 2D electrodes advance the understanding of the 2D/PZT interface and provide solutions for developing high-performance ferroelectrics devices.

Ferroelectric memory: state-of-the-art manufacturing and research

Semiconductor industry calls for emerging memory, demonstrating high speed (like SRAM or DRAM), nonvolatility (like Flash NAND), high endurance and density, good scalability, reduced energy consumption and reasonable cost. Ferroelectric memory FRAM has been considered as one of the emerging memory technologies for over 20 years. FRAM uses polarization switching that provides low power consumption, nonvolatility, high speed and endurance, robust data retention, and resistance to data corruption via electric, magnetic fields and radiation. Despite the advantages, market share held by FRAM manufacturers is insignificant due to scaling challenges. State-of-the-art FRAM manufacturing is studied in this paper. Ferroelectric capacitors and memory cells made by main commercial FRAM manufactures (Texas Instruments, Cypress Semiconductor, Fujitsu и Lapis Semiconductor) are explored. All memory cells are based on the lead zirconate titanate PZT capacitor with the thickness of about 70 nm and IrOx/Ir or Pt electrodes. The leading FRAM technology remains the 130 nm node CMOS process developed at Texas Instruments fabs. New approaches to further scaling and new devices based on ferroelectrics are reviewed, including binary ferroelectrics deposited by ALD techniques, piezoelectronic transistors, ferroelectric/2D-semiconductor transistor structures, and others. Whether FRAM technology will be able to resolve one of the main contradictions between a high-speed processor and a relatively slow nonvolatile memory depends on the success of the new technologies integration.

Programming-Pulse Dependence of Ferroelectric Partial Polarization: Insights From a Comparative Study of PZT and HZO Capacitors

The programming of partial polarization in ferroelectric (FE) hafnium zirconate (HZO) capacitors is shown to depend on the delay between FE reset and the polarization write pulse (delay-before-write), revealing a subtle history dependence. Programming is substantially independent of delays inserted after the write and before the read (delay-before-read), with no decay in partial polarization observed from $1~\mu \text{s}$ up to 260 ms. We further show that nonsaturation in FE polarization can be introduced if the pulse protocol is not strictly symmetric, where strictly symmetric means that the integral of the voltage waveform over a single measurement cycle is zero. The delay-before-write dependence in HZO is compared with lead-zirconium-titanate (PZT) capacitors used in FE random access memory (FRAM) which shows much weaker dependence. The delay dependence is attributed to the dynamics of subcritical nuclei formation in nucleation limited switching. For the first time, the decay of subcritical nuclei in HZO is shown to be observable up to 1 s, and an upper bound on their volume is estimated to be ~10 nm3, corresponding to $\sim {4}\times {4} \times {4}$ unit cells.

Compact model for PZT ferroelectric capacitors with voltage dependent switching behavior

A simple network, consisting of a resistor in series with multiple ferroelectric capacitors in parallel, each in series with a dependent voltage source, is constructed to model ferroelectric capacitors. The material parameters based on the Landau–Khalatnikov equation for the lead zinconate titanate (PZT) capacitor are extracted from measured polarization versus electric field characteristics. A compact model is developed to describe the voltage dependence of PZT capacitors, and calibrated to experimental data. Such voltage dependence is attributed to the voltage dependent interaction force between adjacent domains.

Ferroelectric properties of the flexible Pb(Zr0.52Ti0.48)O3 thin film on mica

High-quality Pb(Zr0.52Ti0.48)O3 (PZT) thin film was fabricated by pulsed laser deposition on flexible mica substrates. X-ray diffraction results showed that the growth of PZT thin film is extended along (001) preferred orientation without any other secondary phases. The electrical properties measurements show that the flexible PZT thin films possess excellent ferroelectric and piezoelectric properties. The remnant polarization (2Pr) and the piezoelectric coefficient (d33) were measured to be 32 μC/cm2 and 15 pm/V, respectively, when the flexible thin film was unbending. Furthermore, the flexible PZT thin films exhibit high stability under mechanical bending. The saturated polarization and dielectric constant of PZT capacitors decrease when the capacitors change from the central area to the edge under a certain bending state. This was interpreted based on the out-of-plane tensile strain change for each capacitor.

Experimental Details of a Steep-Slope Ferroelectric InGaAs Tunnel-FET With High-Quality PZT and Modeling Insights in the Transient Polarization

The steep-slope ferroelectric tunnel-FET (SS-FeTFET), consisting of an InGaAs TFET with a sub-60 mV/dec subthreshold swing (SS) at room temperature and an externally connected high-quality single-crystalline PZT capacitor, displays improved SS compared to the standalone TFET. In this article, we describe the measurement procedure and measurement results of this SS-FeTFET in great detail. To quantitatively extract the ferroelectric (FE) polarization during voltage sweeps, device simulations of the TFET are combined with the SS-FeTFET measurement results. Finally, qualitative insight in some peculiarities of the experimental observations is given, such as the apparent coercive voltage that is larger in the SS-FeTFET than in the standalone FE, the shape of the polarization during voltage sweeps, and the small polarization hysteresis loop at voltages close to the apparent coercive voltage.

Negative Capacitance as Universal Digital and Analog Performance Booster for Complementary MOS Transistors

Boltzmann electron energy distribution poses a fundamental limit to lowering the energy dissipation of conventional MOS devices, a minimum increase of the gate voltage, i.e. 60 mV, is required for a 10-fold increase in drain-to-source current at 300 K. Negative Capacitance (NC) in ferroelectric materials is proposed in order to address this physical limitation of CMOS technology. A polarization destabilization in ferroelectrics causes an effective negative permittivity, resulting in a differential voltage amplification and a reduced subthreshold swing when integrated into the gate stack of a transistor. The novelty and universality of this approach relate to the fact that the gate stack is not anymore a passive part of the transistor and contributes to signal amplification. In this paper, we experimentally validate NC as a universal performance booster: (i) for complementary MOSFETs, of both n- and p-type in an advanced CMOS technology node, and, (ii) for both digital and analog significant enhancements of key figures of merit for information processing (subthreshold swing, overdrive, and current efficiency factor). Accordingly, a sub-thermal swing down to 10 mV/decade together with an enhanced current efficiency factor up to 105 V−1 is obtained in both n- and p-type MOSFETs at room temperature by exploiting a PZT capacitor as the NC booster. As a result of the subthreshold swing reduction and overdrive improvement observed by NC, the required supply voltage to provide the same on-current is reduced by approximately 50%.

Reliability testing of integrated low-temperature PVD PZT films

Reliability and integration of Lead Zirconate Titanate (PZT) is still a strong concern regarding its commercialization. In this work an approach to include reliability on wafer-level for integration and process development is presented. Long-term leakage current development with high statistics of integrated low-temperature PVD PZT capacitors at different temperature, voltage and polarity are discussed. Strong similarities to the behavior of pulsed laser deposition (PLD), sol-gel and ceramic PZT were obtained. It is proposed to use the current evolution after first breakdown as possible indication of remaining useful life. Changes of the Weibull slope above a temperature of 150 °C and gradual change over voltage acceleration in the range of 100 kV/cm to 200 kV/cm were found. This indicates that accelerated lifetime testing in the temperature range below 150 °C is possible and caution is required for voltage acceleration.

Effect of hysteretic and non-hysteretic negative capacitance on tunnel FETs DC performance

This work experimentally demonstrates that the negative capacitance effect can be used to significantly improve the key figures of merit of tunnel field effect transistor (FET) switches. In the proposed approach, a matching condition is fulfilled between a trained-polycrystalline PZT capacitor and the tunnel FET (TFET) gate capacitance fabricated on a strained silicon-nanowire technology. We report a non-hysteretic switch configuration by combining a homojunction TFET and a negative capacitance effect booster, suitable for logic applications, for which the on-current is increased by a factor of 100, the transconductance by 2 orders of magnitude, and the low swing region is extended. The operation of a hysteretic negative capacitance TFET, when the matching condition for the negative capacitance is fulfilled only in a limited region of operation, is also reported and discussed. In this late case, a limited improvement in the device performance is observed. Overall, the paper demonstrates the main beneficial effects of negative capacitance on TFETs are the overdrive and transconductance amplification, which exactly address the most limiting performances of current TFETs.

Current–Voltage Characteristics of Commercial Ferroelectric Capacitors: Deviations from the Preisach Model

The hysteresis properties of ferroelectric PZT capacitors were investigated by measuring their cyclic current–voltage characteristics using a source-measure unit of a semiconductor device analyzer. The first-order reversal curve diagrams were obtained, which have a typical appearance for ferroelectric materials. Based on the obtained diagrams, the degree of correlation between the positive and negative coercive fields of ferroelectric domains was identified, and the deviations in their behavior from the Preisach model domains were determined. A peak-splitting phenomenon was observed, and some of its features were found.

Process induced poling and plasma induced damage of thin film PZT

This paper treats processing sequence induced changes on PZT. Two kinds of metal-PZT-metal capacitors are compared. The top surface and sidewall of PZT in one kind of capacitor is directly bombarded by energetic particles during ion milling process, whereas PZT in the other kind of capacitor is not. The polarity of plasma charging may depend on the ion milling parameters and influence the self-poling of virgin PZT capacitors. Direct ion bombardment induces a significant decrease of PZT permittivity. The PZT reliability (both RVS and TDDB) at positive voltage worsens because of bombardments of energetic particles; whereas the PZT reliability at negative voltage is not influenced. It indicates that the process induced positively charged defects present in the upper part of the capacitor structure initiate the dielectric breakdown.

Magnetodielectric coupling in Ferromagnetic/Ferroelectric/Ferromagnetic spin capacitor

ABSTRACTFerromagnetic/Ferroelectric/Ferromagnetic (Ni/PZT/Ni) tri-layer artificial multiferroelectric structures in spin capacitor configuration were fabricated by sputtering ferromagnetic electrodes on PZT. Magnetocapacitance, magnetoimpedance, and phase angle measurements were carried out by a wide range of frequencies and magnetic fields at room temperature. We also compared the magnetodielectric measurements with Ni/PZT/Ag and Ag/PZT/Ag tri-layers structures. Ni/PZT/Ni spin capacitor shows a significantly different behavior compared to conventional PZT capacitor with Ag electrode and mixed electrode capacitor with one ferromagnetic and one conventional electrode.

Timing A Pulsed Thin Film Pyroelectric Generator For Maximum Power Denisty

Pyroelectric thermal-to-electric energy conversion is accomplished by a cyclic process of thermally-inducing polarization changes in the material under an applied electric field. The pyroelectric MEMS device investigated consisted of a thin film PZT capacitor with platinum bottom and iridium oxide top electrodes. Electric fields between 1-20 kV/cm with a 30% duty cycle and frequencies from 0.1 - 100 Hz were tested with a modulated continuous wave IR laser with a duty cycle of 20% creating temperature swings from 0.15 - 26 °C on the pyroelectric receiver. The net output power of the device was highly sensitive to the phase delay between the laser power and the applied electric field. A thermal model was developed to predict and explain the power loss associated with finite charge and discharge times. Excellent agreement was achieved between the theoretical model and the experiment results for the measured power density versus phase delay. Limitations on the charging and discharging rates result in reduced power and lower efficiency due to a reduced net work per cycle.

Transfer Methods of PZT Thin Capacitor to Flexible Polymer by Self‐Assembled Monolayers

SUMMARYThis paper describes the fabrication method that a lead zirconate titanate (PZT) thin film capacitor, which is formed on a Si substrate by metal organic decomposition (MOD), can be easily transferred to flexible polymer (polydimenthylsiloxane; PDMS) without additional chemical contamination. The thin film capacitor is composed of sandwich structure of PZT between two metal layers. To embed the capacitor structure in the polymer substrate by dry peel‐off process, three kinds of self‐assembled monolayers (SAMs) were investigated for adhesion or antiadhesion layer between metal, polymer, and Si substrate, respectively. Also, the MOD's annealing process with SAMs for PZT lamination was investigated. As a result, the PZT capacitors of 1 μm thickness with a perovskite structure were successfully transferred and embedded in PDMS substrate. These results will be useful for fabricating MEMS devices and integration technology of electrical device to a polymer substrate such as capacitors in three‐dimensional integration or for flexible electronics.

Fabrication of doped Pb(Zr,Ti)O 3 capacitors on Pt substrates with different orientations

The effects of crystallographic orientation on the ferroelectric properties of Pb(Zr,Ti)O3 (PZT) thin films grown on (111) and (100)-oriented Pt substrates are investigated. The effects of doping PZT with species X (forming PXZT) thin films (Pb:X:Zr:Ti, 113:3:30:70; X = La, Nb, or Y) using chemical solution deposition were studied. The crystallinity of all PXZT films was almost identical. The remnant polarisation of the un-doped, La-, Nb-, and Y-doped PZT capacitors with Pt(111) bottom electrodes were 133.4, 64.7, 60.2, and 98.4 µC/cm2, respectively. In ferroelectric capacitors with Pt(100) bottom electrodes, the remnant polarisations were 185.6, 148.1, 103.1, and 135.7 µC/cm2, respectively. The remnant polarisation was larger with Pt(100) than with Pt(111). The initial remnant polarisation of the un-doped PZT capacitors was larger than that of PXZT.

Multi-breakdown model for explaining the formation and growth of black spots in PZT capacitor under DC bias

Lead zirconate titanate (PZT) is widely used in various electro-mechanical devices because of its piezoelectric function. In some of its applications, the piezo ceramic will be subjected to a DC bias. The applied DC bias will stress the PZT ceramic and can undergo an electrical degradation process. This electrical degradation process demonstrates itself as resistance decreases and leakage current increases. Therefore, the electrical degradation phenomenon can severely impact on device performance and reliability. It has been found that, accompany this electrical breakdown process, black spots will appear in the ceramic body. In this paper, the formation and growth of the black spots in a PZT capacitor under DC bias is investigated. The black spot area is further characterized with various analytical methods. Based on previous research, a multi-breakdown model is proposed for explaining the mechanism of black spot growth.

Comparison between the ferroelectric/electric properties of the PbZr0.52Ti0.48O3 films grown on Si (100) and on STO (100) substrates

Ferroelectric/electric properties of PbZr0.52Ti0.48O3 (PZT) thin films grown by pulsed laser deposition (PLD) on two different substrates, Si (001) and SrTiO3 (STO) (001), were comparatively analyzed. The structural characterization has revealed the epitaxial relationship between the grown layers and the two types of substrates, with larger density of structural defects for the films deposited on Si (001) with buffer STO layer. The ferroelectric/electric properties are also different, with lower remnant polarization (about half of the value obtained on STO substrate), higher dielectric constant (about two times larger), and lower leakage current (about two orders of magnitude lower) for the PZT films deposited on Si (001) compared to those deposited on (001) STO substrates. Nevertheless, the results show that the use of a STO buffer layer on Si can be a solution to obtain good quality PZT capacitor structures without using expensive single-crystal oxide substrates. In this way, applications based on PZT capacitors (e.g. non-volatile memories, pyroelectric detectors, light switches, etc.) would be more easily integrated directly on Si wafers.

PZT薄膜キャパシタの作製及び自己組織化単分子膜を用いた樹脂基板への転写手法

This paper describes the fabrication method that a lead zirconate titanate PZT thin film capacitor, which is formed on a Si substrate by metal organic decomposition MOD, can be easily transferred to flexible polymer polydimenthylsiloxane; PDMS without additional chemical contamination. The thin film capacitor is composed of sandwich structure of PZT between two metal layers. To embed the capacitor structure in the polymer substrate by dry peel-off process, three kinds of self-assembled monolayers SAMs were investigated for adhesion or antiadhesion layer between metal, polymer, and Si substrate, respectively. Also, the MOD's annealing process with SAMs for PZT lamination was investigated. As a result, the PZT capacitors of 1 µm thickness with a perovskite structure were successfully transferred and embedded in PDMS substrate. These results will be useful for fabricating MEMS devices and integration technology of electrical device to a polymer substrate such as capacitors in three-dimensional integration or for flexible electronics.

Tunable photovoltaic effects in transparent Pb(Zr0.53,Ti0.47)O3 capacitors

We report an investigation on optical, ferroelectric, and photovoltaic properties of transparent Sn-doped In2O3 (ITO)/Pb(Zr0.53,Ti0.47)O3 (PZT)/ITO thin film capacitors. The ferroelectric PZT sandwiched structures grown on glass substrates exhibit a transmittance of 65% in the visible light range. The current-voltage characteristics show that the transparent PZT capacitors possess a significant photovoltaic response under a light illumination. Moreover, the photovoltaic response can be well tuned by an external electrical field, which can be understood by considering the tunable depolarized field in the PZT capacitors.