Current Development Status and Future Challenges of Ferroelectric Random Access Memory Technologies

A retention analysis method for ferroelectric random access memory (FeRAM) was developed, in which read signal voltages from memory cells are measured. The method uses on-chip sample/hold circuits, an off-chip A/D converter, and memory large-scale integration testing equipment. FeRAM chip retention lifetime can be estimated on the basis of FeRAM read signal voltages after retention periods of one day and upwards. When used as a tool to estimate long-term data retention in FeRAM chips and to analyze fluctuations in memory cell characteristics, this method can provide useful information about FeRAM reliability.

Ferroelectric-based nonvolatile memory (FeRAM) is now a mainstream product category supported by Ramtron, Fujitsu, Texas Instruments, IBM, and Matsushita. The internal array of ferroelectric capacitors in FeRAMs consumes absolutely no energy when the chip is powered. This lack of energy consumption combined with SRAM-like operation at SRAM speeds constitutes a unique advantage for FeRAM memory in low-power embedded applications. Because the ferroelectric technology is buried deep inside the IC package surrounded by digital interface circuits, the true nature of ferroelectric memory capacitor operation is obscured from the user. It is possible to operate a simple ferroelectric nonvolatile memory from the I/O pins of a microprocessor using discrete ferroelectric capacitors in a Sawyer-Tower circuit configuration. Designing and operating a ferroelectric memory with discrete capacitors provides insight into the nature of FeRAMs, their internal operation, and their reliability. The read and write times of the discrete memory will be fast, limited only by the current capacity of the I/O pins. The discrete ferroelectric capacitors will retain their written state without concern for whether the microcontroller is powered or not. Unlike EEPROM or FLASH transistors, discrete ferroelectric capacitors can be physically handled during retention without corrupting their stored states.

Capacitance extraction of ferroelectric HfO2 capacitors was characterized at a frequency of 1 GHz. By applying a bias voltage in the non-switching region of the ferroelectric HfO2 films, a varactor operation was confirmed. Introduction The ferroelectric HfO2 layer has attracted attraction in CMOS and memory applications due to its scaling ability and process compatibility. Generally, ferroelctric capacitors show increase in the capacitance near the coercive field. By setting a proper bias to the ferroelectric capacitors, they can work as varactors under non-switching mode. As there is an increasing demand on-chip varactors for monolithic microwave ICs (MMICs) [1,2]. In this research, we measured the capacitance of the ferroelectric HfO2 capacitors at high frequency and confirmed the capacitance control. Measruements were done under on-wafer probing system in the frequency range of 10 MHz to 1 GHz [3]. Experiments Figure 1 shows the schematic cross-section of ferroelectric HfO2 capacitors. A 1 mm plasma SiO2 layer was first deposited on a high-resistive Si wafer f. A 12-nm-thick 5 mol% Y-doped HfO2 film were deposteid by atomic layer deposition (ALD). The top and bottom electrode were both W deposited by sputtering and patterned by reactive ion etching (RIE). Annealing to transform the HfO2 layer into ferroelectric pahse was conducted at 500 oC. Metal contacts of Au/Ni/Ti were deposited by thermal evaporation. Results and discussions Capacitance-voltage measurement taken from LCR meter at 10 kHz is shown in fig. 2. After polling process, the capacitance can be tuned by 32 % by controlling the bais voltage in the non-switching region. The capacitance values under different bias voltage, extracted from the S-parameters of capacitors with proper calibration patterns, are shown in fig. 3. Although the capacitance tuning was narrow compared to those obtained by the LCR meter, the varactor operation was confirmd with ferroelectric HfO2 capacitors. Conclusion A varactor operation in ferroelectric HfO2 capacitor at 1 GHz was confirmed.

Effect of porous silicon substrate on structural, mechanical and optical properties of MOCVD and ALD ruthenium oxide nanolayers

To maintain a modern livelihood, huge amount of energy is needed which are primarily sourced from fossil fuels that causes global warming and has become an environmental concern. The use of renewable and sustainable green energy has been increasing day by day which needs efficient devices for storage and supply of energy on demand. Among the energy storage devices, batteries have a high energy storage density and low power output, while capacitors possess relatively lower energy density but are capable of exhibiting a high-power output. Dielectric capacitors show high-power density, ultra-fast charge-discharge rates and higher efficiency which make them indispensable for application in electronic devices. Dielectric materials used in the commercially available capacitors are mostly lead based ferroelectric and anti-ferroelectric ceramics. As lead is toxic and causes havoc environmental concerns, the usage of lead/heavy metal containing materials is being gradually phased out and alternate lead-free high-performance materials are sought after. Due to difficulties in ceramic synthesis technique, uncontrolled grain growth and other defects are created resulting in poor dielectric properties. This article tries to present lead-free anti-ferroelectric glass-ceramics based dielectrics as an emerging material for catering to the future green energy demands. Lead free glass-ceramics based dielectrics are multifunctional materials with huge potentials for ferroelectric random access memory (FRAM) and photonic applications, besides their prospects as a future energy storage material.

Synthesis and characterization of Zr and Mg doped BiFeO3 nanocrystalline multiferroics via micro emulsion route

Bi4-xLaxTi3O12 (BLT) ferroelectric thin films were prepared on a Pt/TiOx/SiO2/Si substrate using metalorganic decomposition (MOD) method, and their electrical properties were evaluated with thickness, composition and crystallization annealing temperature. Irrespective of the preparation conditions, BLT films were c-axis oriented, and had a dense surface morphology without pore to produce smooth Pt/BLT/Pt interfaces of capacitor. The film thickness was controlled as 90 nm to obtain a low coercive voltage (2Vc) without the problem of capacitor short-fail. The proper composition of Bi3.35La0.85Ti3O12 was selected for the largest switching polarization (P*-P∧), good fatigue endurance and a low leakage current density (JL). After crystallization annealing at 700°C, the optimized film of 90 nm Bi3.35La0.85Ti3O12 showed the good electrical properties, such as 2Vc of 2.0 V, P*-P∧ of 13 µC/cm2, JL of 1×10-6 A/cm2 at a applied voltage of 3 V and no polarization loss up to 1×1011 fatigue cycles, for ferroelectric random access memory (FeRAM) application.

We have investigated the cell signal distributions of ferroelectric random access memories (FeRAMs) using newly developed design scheme, hybrid bit line architecture and their reliability against imprint degradation. Since FeRAMs have relatively large signal distributions due to nonuniform ferroelectric storage capacitors, cell signal interference between neighboring bit lines severely degrades the sensing signal margin. In order to remove the cross-talk noise, hybrid bit line architecture is developed, which is a combination of the conventional folded and open bit line schemes. The lifetime against imprint degradation of FeRAM devices is also increased using hybrid bit line architecture.

Influence of metal electrodes on the irradiation resistance of HZO ferroelectric thin film capacitors and mechanism analysis

The polarization reversal in ferroelectric HfO 2 is adopted to store information in three distinct device classes – ferroelectric field effect transistors (FeFET), ferroelectric capacitors (FeCAP) and ferroelectric tunnel junctions (FTJ). Common to all three concepts is the adoption of a ferroelectric layer stack that acts either as gate dielectric in the FeFET or as the capacitor dielectric and tunneling barrier in the FeCAP or FTJ, respectively. A composite structure including an inevitably or purposefully formed dielectric layer is frequently adopted. In this work we report on the co-existence of all three memory concepts within one device structure and propose a 2T1C ferroelectric memory cell that allows the operation and comparative characterization of the trinity of ferroelectric memory devices.

Elastomeric primer and adhesive systemSection:ChooseTop of pageElastomeric primer and ad... <<Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Master Bond X21Med is a single-component elastomeric compound that passes ISO 10993-5 tests for cytotoxicity. It was developed as a primer to promote adhesion between polyolefins and other surfaces such as metals, ceramics, composites, and other kinds of plastics, but it can also bond two polyolefin materials. Easy to use, X21Med has a low viscosity of less than 250 cps. It cures at ambient temperatures; with heat, it cures more rapidly. It is serviceable from −51 °C to 93 °C. As a primer, X21Med should be applied in a thin layer to the surface and then the solvent allowed to evaporate. 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Master Bond Inc, 154 Hobart St, Hackensack, NJ 07601, www.masterbond.com Atomic layer deposition plasma-processing systemSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p... <<Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Oxford Instruments has announced the novel FlexAL-2D system for atomic layer deposition (ALD) of 2D transition-metal dichalcogenides for nanodevice applications. The FlexAL-2D system implements plasma-enhanced ALD to synthesize layers of 2D molybdenum disulfide films with tunable morphologies—namely, in-plane and vertically standing nanoscale architectures on CMOS-compatible silicon dioxide and silicon substrates. 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Oxford Instruments plc, 300 Baker Ave, Ste 150, Concord, MA 01742, www.oxford-instruments.com Cold cathode vacuum transducerSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans... <<X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES The MKS Granville-Phillips 523 wide-range cold cathode vacuum transducer is suitable for applications that require an economical cold cathode with limited accuracy for simple, repeatable pressure measurement. It combines diverse materials and two types of discharge. The 523 covers a wide pressure range from 10−7 torr to atmosphere without the use of a conventional heat-loss Pirani sensor. A high-pressure discharge cell makes a second vacuum sensor unnecessary. The device can be mounted in any orientation, has a simple analog output, and complies with Restriction of Hazardous Substances and CE standards. Applications include analytical equipment such as mass spectrometers, scanning electron microscopes, industrial coating systems, and general vacuum-based pressure measurement apparatus. MKS Instruments Inc, 2 Tech Dr, Ste 201, Andover, MA 01810, www.mksinst.com X-ray fluorescence systemSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence system <<Precision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Bruker has announced its S8 Tiger Series 2 wavelength dispersive x-ray fluorescence (WDXRF) system for advanced quantitative elemental analysis in academic and industrial research and materials quality control. 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Bruker AXS GmbH, Oestliche Rheinbrueckenstr 49, 76187 Karlsruhe, Germany, www.bruker.com Precision UV mirrorsSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrors <<Solder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Edmund Optics offers its TechSpec precision UV mirrors in deep-UV (DUV) and new vacuum-UV (VUV) enhanced coatings. They are suitable for use in numerous optical setups to reflect UV light, including fluorescence microscopy and spectrometry, and for various commercially available light sources. The mirrors with DUV coating offer excellent reflection from 190 nm to long-wave IR (LWIR), and the VUV-coated mirrors provide optimized reflection from 120 nm to LWIR. 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Intlvac Thin Film Corporation, 1401 Duff Dr, Unit 600, Fort Collins, CO 80524, www.intlvac.com Liquid transfer pumpSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pump <<New literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES KNF has designed an economical solenoid-driven diaphragm pump for OEM users. The FL 10 pump features a nominal liquid flow rate of 100 mL/min against atmospheric pressure, simple linear flow rate adjustment, and a maintenance-free expected lifetime of 10 000 h. It can be operated to 14.5 psig (1 bar). Spring tension in the linear solenoid drive keeps the flow through the FL 10 tight in both directions when turned off and makes additional check valves unnecessary. 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Hiden Analytical Inc, 37699 Schoolcraft Rd, Livonia, MI 48150, www.hideninc.com Ellipsometer for thin-film measurementsSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil... <<Specialized vacuum gauges...CITING ARTICLES According to Horiba Scientific, its Uvisel Plus modular ellipsometer includes a new generation of the FastAcq acquisition technology, which can measure thin-film samples faster and more accurately than previously possible. The technology features new electronic data processing and a high-speed monochromator. Samples from 190 nm to 2100 nm can be measured within 3 min at high resolution. The technology allows for continuous adjustment of the spectral resolution along the measurement range. 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Ferroelectricity exhibits two stable states with permanent polarizations, making it promising for nonvolatile memory applications. Compared to conventional perovskite ferroelectrics, hafnium-based ferroelectric materials, such as Hf0.5Zr0.5O2 (HZO), attracts much attention due to their compatibility with CMOS technology [1]. Furthermore, with the high demand in high-performance computing and the emerging quantum computing, cryogenic memory technologies become more important due to the required much lower operational temperatures. In this work, we investigate the properties of HZO-based ferroelectric capacitors and characterize ferroelectric field-effect transistors (FeFETs) from 300 K to 4 K.A 10-nm HZO layer was deposited by atomic layer deposition (ALD) to serve as the ferroelectric layer in both capacitors and FeFETs (Fig. 1). For the ferroelectric capacitors, 75-nm TiN was deposited by sputtering for the bottom and top electrodes, which provides tensile stress to the HZO layer and facilitates the formation of the ferroelectric phase [2]. Similarly, in FeFETs, a 75-nm TiN is deposited as the gate metal. Subsequent rapid thermal annealing (RTA) steps were performed at 650 °C for 30 seconds in forming gas to form the ferroelectric orthorhombic phase. For the FeFETs, different gate stacks were deposited: a 10-nm HZO layer (MFS structure) or a combination of a 10-nm HZO layer and a 1-nm Al2O3 interlayer (IL) between the HZO and the Si substrate to improve the interface quality (MFIS structure).For ferroelectric capacitors, the polarization vs. voltage (P-V) results are measured at temperatures from 300 K to 4 K (Fig. 2(a)). The extracted remnant polarization (2Pr) and coercive voltage (2Vc) are shown in Fig. 2(b). 2Pr value decreases with a reducing temperature due to the reduced mobility of oxygen vacancies, leading to weaker polarizations in cryogenic environments [3]. 2Vc increases with a decreasing temperature, which means that a higher voltage is required to switch the polarization direction at lower temperatures [4]; that is, polarization switching becomes more challenging.MFS and MFIS FeFETs were also characterized at 300 K to 4 K. The Id-Vg results with various gate sweeping ranges of MFS and MFIS FeFETs at 300 K are shown in Fig. 3. We observed a competition between ferroelectric polarization switching (counter-clockwise Id-Vg hysteresis loops) and charge trapping effects (clockwise Id-Vg hysteresis loops). To further analysis, we define the required gate bias with zero hysteresis (Vsweep at ΔVth = 0) as the voltage where ferroelectricity starts to dominate. For MFIS FeFETs, the required sweep bias is larger than that of MFS FeFETs, which suggests that a higher applied voltage is needed to switch the dipoles in MFIS FeFETs. This is because a portion of the applied voltage drops across the IL, thereby decreasing the electric field in the ferroelectric layer. Furthermore, there’s an internal depolarization field induced by Al2O3 IL, which opposes the polarization in the ferroelectric layer and reduces its polarization [5]. As the scan range of gate bias becomes larger, MFS FeFETs exhibit stronger ferroelectricity (counter-clockwise hysteresis with a negative ΔVth) (Fig. 4(a)). As the temperature decreases, the required scan range of gate biases becomes much larger, which makes the HZO films more difficult to convert to ferroelectric phases. In contrast, MFIS FeFET shows counter-clockwise hysteresis only at 300 K (Fig. 4(b)), below which charge trapping effects dominate over polarization switching even under a sweep voltages up to 5 V. This trend is consistent with the results in ferroelectric capacitors, where higher voltages are required for polarization switching at lower temperatures. Acknowledgements This work was supported by the Powerchip Semiconductor Manufacturing Corporation (PSMC) of Taiwan (grant No: 113H1004-C15), the National Science and Technology Council (NSTC 113-2119-M-002-022-), and the Center of Data Intelligence: Technologies, Applications, and Systems, National Taiwan University (grant No: 113L900903). References Müller et al., IEDM, 10.8 (2013).Si Joon Kim et al., Appl. Phys. Lett. 111, 242901 (2017).Starschich et al., Appl. Phys. Lett. 108, 032903 (2016).Stephen Ducharme et al., Phys. Rev. Lett. 84, 175 (2000).Patrick D. Lomenzo et al., Non-Volatile Memory Technol. Symp., 1 (2019). Figure 1

Preparation of copper films by metal organic chemical vapor deposition on various substrates

PbZr(x)Ti(1-x)O3 (PZT) thin films were deposited on 3-dimensional (3D) nano-scale trench structures for use in giga-bit density ferroelectric random access memories. PZT thin films were deposited by liquid delivery metalorganic chemical vapor deposition using Pb(thd)2, Zr(MMP)4, and Ti(MMP)4 precursors dissolved in ethyl cyclohexane. Iridium thin films were deposited by atomic layer deposition, and they exhibited excellent properties for capacitor electrodes even at a thickness of 20 nm. The trench capacitor was composed of three layers, viz. Ir/PZT/lr (20/60/20 nm), and had a diameter of 250 nm and a height of 400 nm. Almost 100% step coverage was obtained at a deposition temperature of 530 degrees C. The PZT thin film capacitors with a thickness of 60 nm on a planar structure exhibited a remnant polarization (Pr) of 28 microC/cm2, but the Pr value of the 3D PZT capacitors decreased slightly with decreasing 3D trench pattern size. The transmission electron microscope analysis indicated that the PZT thin films had compositional uniformity in the 3D trench region. Both columnar and granular grains were formed on the sidewalls of the trench capacitors, and their relative proportion exhibited strong size dependence. The trench capacitors with more columnar PZT grains showed good switching behavior under an external bias of 2.1 V and had a remnant polarization of 19-24 microC/cm2.

Vanadium oxide supported on TiO2(P25) catalysts were synthesized via atomic layer deposition (ALD) of vanadyl acetylacetonate (VO(acac)2). Comprehensive investigations were performed to evaluate the ALD temperature window and the saturation deposition period of VO(acac)2, which were found to be 140–210 °C and 120 min, respectively. The synthesized catalysts were compared to their corresponding impregnation ones for the oxidative dehydrogenation of propane reaction (ODH-P). The ODH-P results indicated the superior performance of the ALD catalysts for the low temperature ODH-P (< 350 °C) given its better dispersion of vanadium oxide(vanadia) in the ALD catalysts. Several characterization techniques including HR-TEM, FE-SEM, XRD, BET, XPS, O2-chemisorption, ICP-OES, and H2-TPR were utilized to evaluate the influence of the ALD and impregnation methods of synthesis on different features of the catalysts. It was observed that the ALD method could offer far better dispersion of the active phase on the support of the catalyst, which is beneficial for the catalytic performance. Variations of Hacac, acetone, and CO2 FTIR absorbance peaks’ areas versus the support temperature