Bottom electrode structures of Pt/Ru and Ru deposited on polycrystalline silicon by MOCVD for DRAM capacitor

Abstract

The electrode structures of Pt/Ru and Ru on polycrystalline silicon (poly-Si) were prepared by metalorganic chemical vapor deposition (MOCVD) for high dielectric constant (Ba, Sr)TiO₃(BST) capacitor integration. The electrode structures of Pt/Ru/poly-Si annealed above 700°C for 1h in oxygen atmosphere showed a smooth surface ·microstructure without any second phases on the platinum. The specific contact resistance of Pt/Ru and poly-Si in Pt/Ru/poly-Si structures annealed at 800°C was about 1.5 × 10^?5 Ω-cm². The step coverage of Ru film deposited at 150°C was 76% and those of Pt film deposited at 300°C on Ru (deposited at 150°C) was about 61.3%.     

The Effect of the Oxygen Exchange at Electrodes on the High-Voltage Electrocoloration of Fe-Doped SrTiO3 Single Crystals: A Combined SIMS and Microelectrode Impedance Study

The effect of the electrode material on the high voltage stoichiometry-polarization (electrocoloration) of Fe-doped SrTiO₃ single crystals has been studied. For different electrode materials (150-nm Ag/15-nm Cr and 150-nm Au/15-nm Cr) secondary ion mass spectrometry (SIMS) was used to measure the depth profile of the ¹⁸O-isotope after high-field stress. The results were compared with spatially resolved impedance measurements on electrocolored Fe-doped SrTiO₃ single crystals. For Au/Cr as well as Ag/Cr electrodes a large dc voltage leads to moving color fronts which are usually correlated with a pronounced stoichiometry polarization of the samples due to electrodes blocking the ionic current. However, the local impedance measurements demonstrate that the conductivity profiles near the cathode depend on the electrode material. This finding is in accordance with the SIMS measurements which indicate that the Ag/Cr-electrodes are, in contrast to Au/Cr-electrodes not completely inactive for the oxygen incorporation into the Fe-doped SrTiO₃. The results are discussed in terms of defect chemical models.     

Structure,Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba_0.70Ca_0.30TiO₃-(BCT),Ba(Zr_0.2Ti_0.8)O₃-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.     

Electrical properties of 3-component piezoelectric thick films by screen printing method

Abstract

PZT(52/48) thick films with Pb-based complex oxide (PCW) additive were prepared on Pt/TiO₂/YSZ/SiO₂/Si substrate by screen printing method. PCW addition and PZT sol application are performed to fabricate high density PZT thick film and to lower sintering temperature. With the increase of sintering temperature, electrical properties of screen-printed films were improved. Further, for the sol-gel treated thick films, the electrical properties were improved as compared to only screen-printed films. For the PZT-0.12PCW thick films with sol-treated and sintered at 900°C, the remanent polarization (P_r) was about 23.8 μC/cm² at the applied filed of 150 kV/cm², the dielectric permittivity (Ω_r) was 1024 at the frequency of 100 kHz, and the piezoelectric coefficient (d₃₃) was 339 pC/N at the applied pressure of 1 atm. Finally, the application of these PZT thick films to piezoelectric actuator is described.     

A 14b 150 MS/s 140 mW 2.0 mm2 0.13µm CMOS A/D converter for software‐defined radio systems

This work proposes a 14 b 150 MS/s CMOS A/D converters (ADC) for software‐defined radio systems requiring simultaneously high‐resolution, low‐power, and small chip area at high speed. The proposed calibration‐free ADC employs a wide‐band low‐noise input sample‐and‐hold amplifier (SHA) along with a four‐stage pipelined architecture optimizing scaling‐down factors for the sampling capacitance and the input trans‐conductance of amplifiers in each stage to minimize thermal noise effect and power consumption. A signal‐insensitive 3‐D fully symmetric layout achieves a 14 b level resolution by reducing a capacitor mismatch of three MDACs. The prototype ADC in a 0.13µm 1P8M CMOS technology demonstrates a measured differential nonlinearity (DNL) and integral nonlinearity within 0.81LSB and 2.83LSB at 14 b, respectively. The ADC shows a maximum signal‐to‐noise‐and‐distortion ratio of 64 and 61 dB and a maximum spurious‐free dynamic range of 71 and 70 dB at 120 and 150 MS/s, respectively. The ADC with an active die area of 2.0mm² consumes 140 mW at 150 MS/s and 1.2 V. Copyright © 2010 John Wiley & Sons, Ltd.     

Characteristics of the optical resonator composed of the nonlinear directional coupler

This paper describes a simple method of analysis of an optical resonator composed of a nonlinear directional coupler. Assuming the coupler is made in semiconductor‐doped glass by the K⁺‐ion diffused technique, the transmission and reflection characteristics are calculated and demonstrated. The parameter dependence of the bistability appearing in the transmitted and reflected light is also presented. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 1–10, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20036     

Improvement of loss factor tan δ of PZT PbTi0.75Zr0.25O3 films by O+-Ion-implantation

Abstract

Ion implantation into (111) PZT films was done with 150 keV O⁺-ions using the following doses: 5 · 10¹⁰ cm^?2 and 5 · 10¹³cm^?2. The penetration depth of the O⁺-ion beam (through a 150 nm top Pt-electrode) was calculated with the TRIM. SP program version TRVMC95. For 10⁴ particles, 22% of them were calculated to pass the top Pt electrode, 1% of the 10⁴ particles were calculated to reach a penetration depth of 150 nm in PZT. The O⁺-implantation led to a significant improvement (50%) of loss factor tan δ. This effect is ascribed within current theory to a decrease of oxygen vacancies (defects). Oxygen vacancies are supposed to be associated by Ti³⁺, Ti²⁺ and Ti⁺centers in the perovskite lattice. Evidence for a possible participation of such reduced (charged) titanium defects was obtained by luminescence spectroscopy. Therefore, PZT samples were treated with H₂ to increase the concentration of reduced Tiⁿ⁺ (n<4) ions in the perovskite lattice by chemical treatment. The luminescence spectrum of such reduced samples showed peaks at 3.2, 2.95 and 2.8 eV (surface Ti³⁺, Ti²⁺ Ti⁺ centers). Furthermore, peaks at 1.87eV and 2.2 eV were observed. These near-midgap states have been ascribed to transitions from Ti³⁺ and Ti²⁺ from the bulk of PZT (3.8 eV excitation energy, T = 6K). Finally, a sharp luminescence peak at 3.34 eV (6K) is assigned as self-trapped exciton luminescence.     

Thermoelectric rectification in a graphene-based triangular ballistic rectifier (G-TBR)

A four-terminal ballistic rectifier demonstrating voltage rectification for both electrical (AC/DC) as well as thermal (temperature gradient) inputs is presented. The thermoelectric behavior of the graphene triangular ballistic rectifier (G-TBR) is based on its nonlinear electrical response. The responsivity and noise equivalent power of the device are calculated to be 8870 mV/W and 1.59 nW/Hz^1/2, respectively, at a back-gate voltage of 5 V. The rectified thermal voltage between two isothermal output (lower and upper) terminals is estimated to be 2.8 µV at a temperature gradient of 150 K. Further, the electric and thermoelectric output of the proposed G-TBR is validated by analytical modeling. Such G-TBRs could be used in the future in energy harvesting application to use heat produced by electronic circuitry, integrated circuits (ICs), etc.

     

The magnitude of signal errors introduced by ISIS in quantitative31P MRS

It is well known that the quality of a quantitative³¹P MRS measurement relies largely on the performance of the volume selection method, and that image selected in vivo spectroscopy (ISIS) suffers from contaminating signal caused mostly by Tl smearing. However, these signal errors and their magnitude are seldom addressed in clinical studies. The aim of this study was therefore to investigate the magnitude of signal errors in³¹P MRS when using ISIS. The results from the measurements with a homogeneous head phantom are as follows: at low TR/T1 ratios the contamination increases rapidly, especially for small (< 27 cm³) VOI sizes; at TR/T1 = 1, the signal from a 27 cm³ VOI was 20% too high, and from an 8 cm³ VOI 150% too high. The signal obtained from different VOI positions varied between 80 and 127%. The signal varied linearly with the³¹P concentration in the object. However, a too high signal was obtained when the concentration was lower in the region of interest (inner container) than in the rest of the phantom. The agreement between the simulations and measurements shows that the results of this study are generally applicable to the measurement geometry and the ISIS experiment order rather than being specific for the MR system studied. The errors obtained both experimentally and in computer simulations are too large to be ignored in clinical studies using the ISIS pulse sequence.     

Nano vanadyl‐phthalocyanine crystals fabricated on KBr substrate

Vanadyl‐phthalocyanine (VOPc) thin films deposited on a KBr substrate by molecular beam epitaxy (MBE) consist of nano‐VOPc crystals epitaxially grown. The nano‐VOPc crystals acquire a square shape as a result of annealing at 150^°C. The size of the nano‐crystals is controllable by changing the conditions of MBE deposition and thermal treatment. The growth processes of nano‐crystals on the KBr substrate are elucidated experimentally and are shown to be closely related to strong interaction between the VOPc molecules and the KBr substrate. Their mechanisms can be explained in terms of surface diffusion of the VOPc molecules on the KBr substrate. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 41–48, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20645     

Pulsed Laser Deposition of Ba0.6Sr0.4TiO3 Thin Films and Their Optical Properties

ABSTRACT

Barium strontium titanate [Ba_0.6Sr_0.4TiO₃ or BST (60/40)] thin films were deposited on MgO (100) substrates using pulsed laser deposition. X-ray diffraction (XRD) measurements revealed that the BST thin films had epitaxially grown on the MgO (100) substrates. The surface morphology of the thin films was observed using an atomic force microscope and the grain size was found to be about 100–150 nm. The surface roughness was around 4.9 nm for a 250 nm thick film. The optical transmittance of the BST thin film was measured using a transmission mode ellipsometer. The BST/MgO configuration was highly transparent in the visible region. The optical band gap energy of the BST film, calculated by applying the Tauc relation, was 3.56 eV. Optical waveguide characteristics of the BST (60/40) thin film were determined using a prism coupler. The electro-optic (E-O) properties were measured at 632.8 nm wavelength using a phase modulation detection method. The BST film exhibited a predominately quadratic E-O behavior and the quadratic E-O coefficient was found to be 0.58 × 10^{? 17} m²/V².     

Pulsed excimer laser deposition of ferroelectric thin films

Abstract

Pulsed UV excimer laser ablation was employed to deposit multi-axial, bi-axial and uni-axial ferroelectric compositions of PZT, bismuth titanate and lead germanate respectively. In general, a fluence lower than 2 J/cm² caused a preferential evaporation of volatile components, resulting in stoichiometric imbalance. However, the fluences beyond 2 J/cm² enabled the deposition of stoichiometric thin films of multi-component oxide systems. The intrinsic bombardment due to the energetic ablated species during the thin film deposition seemed to influence the composition, structure, orientation and the electrical properties. The electrical characterization of ferroelectric films indicated a dielectric constant of 800–1000, a P_r of 32μC/cm² and E_c of 130KV/cm for polycrystalline PZT films and the corresponding quantities were measured to be 150, 7 μC/cm² and 20 KV/cm for in-situ crystallized c-axis preferred oriented bismuth titanate films. Lead germanate thin films oriented along c-axis (003) showed a dielectric constant of 30, a P_r of 2.5 μC/cm² and E_c of 55 KV/cm.     

A CMOS voltage regulator for passive RFID tag ICs

A low‐power voltage regulator for passive RFID tag ICs is proposed in this paper. It consists of a self‐biased mutually compensated voltage reference, a low dropout (LDO) voltage regulation circuit and a power‐on‐reset (POR) circuit. It is fabricated in a commercial 0.18?µm CMOS technology and applied to a passive UHF RFID tag IC. The total quiescent current is 700 nA under a 1.8‐V supply. The output voltage of the regulator is 1.45 V with load capability of 50 µA. The temperature coefficients of the voltage reference and the output voltage are only 9 and 43 ppm/^°C, respectively. A POR signal with width pulse of 150 ns is generated for the digital part in the tag IC. Copyright © 2010 John Wiley & Sons, Ltd.     

Reliability assessment of indium tin oxide thin films by accelerated degradation test

The thermal degradation behavior and reliability of indium tin oxide (ITO) thin films deposited on glass substrates using radio frequency (rf) magnetron sputtering were investigated over the temperature range of 200–250^∘C in air. Accelerated degradation test (ADT) was performed to assess the reliability of ITO films. The lifetime of ITO films under normal operating condition (150^∘C) can be predicted to be 1.148 × 10⁵ h via statistical analysis and modeling of data acquired from ADT. The lifetime of ITO films was also evaluated using finite element analysis (FEA) based on the assumption of oxygen diffusion mechanism.     

Low temperature growth of sol-gel SrBi2Ta2O9 thin films by low-pressure annealing

A new low-temperature processing method to prepare SrBi₂Ta₂O₉ thin films is proposed. These thin films were prepared on Pt/Ta/SiO₂/Si substrates by a sol-gel method, and their structural and electrical properties were investigated. Films were annealed before and after the top Pt electrode deposition. The first annealing was performed in a 760-Torr oxygen atmosphere at 600 °C for 30 min, and the second annealing was performed in a 5-Torr oxygen atmosphere at 600 °C for 30 min. The films were well crystallized and fine-grained after the second annealing. The electrical characteristics of the 200-nm-thick film obtained by this new process were as follows: remanent polarization, P_r = 8.5 μC/cm²; coercive field, E_c = 36 kV/cm; and leakage current density, I_L = 1 × 10⁻⁷ A/cm² (at 150 kV/cm). This process is very attractive for highly integrated ferroelectric nonvolatile memory applications. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 27–33, 1997     

Fabrication and characterization of flexible piezoelectric composites with natural rubber matrix

Abstract

This work aims to fabricate and characterize flexible piezoelectric composites with natural rubber (NR) matrix. Different amounts of Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMNT) powders were added in NR matrices. Porosity, tensile strength and percent elongation at break of composites tended to decrease with increasing PMNT content. The dielectric constant of the NR materials was found to be 3.5. It was raised up to 4.2, 5.0, 4.5, 4.8 and 5.1 when 60, 80, 100, 120 and 150 phr PMNT powders were added. However, dielectric loss of NR materials did not change with PMNT additions. Among this composite system, the NR/100PMNT composite showed the best piezoelectric properties, which its output voltage, piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) values were equal to 1.61 V, 2.1?×?10^?4 pC/N and 5.4?×?10^?6 V?m/N, respectively. This composition composite is a promising material suitable for further improvement to be used as piezoelectric generators in energy harvesting applications.     

A pulsed power supply with sag compensation using controlled gradational voltage

A pulsed power supply with sag compensation using controlled gradational voltage to increase the flatness of output waveforms has been developed. The sag compensation circuit consists of compensation units connected in series. Each compensation unit consists of capacitances, diodes, and semiconductor switches. The capacitances of each unit are charged with different voltages by 2ⁿ(V₀,2V₀,4V₀,…). The compensation voltage, which has 2ⁿ?1 steps, is generated by switching the semiconductor switches of each unit in a binary sequence. Using this method, compensation voltage waveforms up to 6.2 kV with 31 steps can be obtained with five compensation units. The sag compensation circuit has been adapted to a direct switch‐type pulsed power supply, which generates 7 kV pulsed voltage with a pulse width of 700µs, thus realizing sag compensation. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 54–63, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20017     

Towards minimum achievable phase noise of relaxation oscillators

A relaxation oscillator design is described, which has a phase noise rivaling ring oscillators, while also featuring linear frequency tuning. We show that the comparator in a relaxation‐oscillator loop can be prevented from contributing to 1/f² colored phase noise and degrading control linearity. The resulting oscillator is implemented in a power efficient way with a switched‐capacitor circuit. The design results from a thorough analysis of the fundamental phase noise contributions. Simple expressions modeling the theoretical phase noise performance limit are presented, as well as a design strategy to approach this limit. To verify theoretical predictions, a relaxation oscillator is implemented in a baseline 65 nm CMOS process, occupying 200 µm × 150 µm. Its frequency tuning range is 1–12 MHz, and its phase noise is L(100kHz) = ?109dBc/Hz at f_osc = 12MHz, while consuming 90 μW. A figure of merit of ?161dBc/Hz is achieved, which is only 4 dB from the theoretical limit. Copyright © 2012 John Wiley & Sons, Ltd.     

Characteristics on electrical resistance change of Ag doped chalcogenide thin film application for programmable metallization cell

Programmable Metallization Cell (PMC) Random Access Memory is based on the electrochemical growth and removal of nanoscale metallic pathways in thin films of solid electrolyte. This paper investigates the resistance change characteristics with applied voltage bias on Ag/Ge–Se and Ag/As–Se chlacogenide thin film structure and describes the electrical characteristics of PMC-RAM made from these materials following annealing at 150 °C. As a result, it was obtained that R _reverse/R _forward ratio which represent by reversible resistance change was about 10⁶, which ratio value can be get a high sensing margin when PMC-RAM detect the data. PMC-RAM technology promises to be non-volatile, low current and potentially, low cost for the next generation of nonvolatile memory application such as RFID chip to replace EEPROM.     

Three‐dimensional numerical analysis on discharge properties of microwave excited ring dielectric line surface wave processing plasma device

A three‐dimensional simulation code with the finite difference time domain (FDTD) method combined with the electron fluid model has been developed for the microwave excited surface wave plasma in the RDL‐SWP device. This code permits the three‐dimensional numerical analysis of the spatial distributions of electric field, power absorption, electron density, and electron temperature. At a low gas pressure (about 10 mTorr), the numerical results were compared with the experimental measurements that show the validity of this 3D simulation code. A simplified analysis assuming that the electron density is spatially uniform has also been studied and its applicability is evaluated by the comparison of the 3D simulation and the analytical solutions. The surface wave eigenmodes are determined by the electron density, and it is found that the structure of the device strongly influences the spatial distribution of the electric fields of surface waves in a low‐density area (n_e < 3.0 × 10¹¹ cm^?3). A method to irradiate by microwave the whole surface area of the plasma is proposed. The method is found to be effective in obtaining a high uniformity distribution of electron density. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 1–12, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10333