Kiyoshi Uchiyama

Low temperature crystallization of SrBi2Ta2O9 (SBT) films

Abstract 650°C process of SrBi2Ta2O9 (SBT) has been achieved through the use of new metal organic deposition (MOD) solution and the optimization of the deposition conditions. The sample showed a high remnant polarization (2Pr) of 14 μC/cm2 @3V, a low leakage current of 10–8 A/cm2 or less @3V, and a fatigue-free nature. We believe this processing will realize high-density FeRAM integration of SBT.

Low temperature crystallization of mocvd deposited sbt films

Abstract An annealing 650°C process for SrBi2Ta2O9 (SBT) has been achieved in metal organic chemical vapor deposition (MOCVD). An optimized post anneal step at 650°C is also included. The samples showed a high remnant polarization (2Pr) of 14 μC/cm2 @5V, low leakage current of 10−8 A/cm2 or less @4V, and a fatigue-free nature. This is the first report of MOCVD deposited SBT that can achieve 650°C crystallization with the post annealing.

Study of AlInP and GaInP grown by gas source molecular beam epitaxy (GSMBE)

The electrical, optical and structural properties of Al0.5In0.5P and Ga0.5In0.5P layers grown on (001) GaAs substrates by gas source molecular beam epitaxy (GSMBE) using phosphine (PH3) gas have been studied. For heavy Be doping, the electrical activity was found to be unity up to atomic Be concentration of 2 × 1018 cm-3 in Al0.5In0.5P and 3 × 1019 cm-3 in Ga0.5In0.5P. The maximum hole concentrations achieved are 3.5 × 1018 cm-3 in Al0.5In0.5P and 4 × 1019 cm-3 in Ga0.5In0.5P. 20 K photoluminescence (PL) measurements for heavily Be-doped Al0.5In0.5P showed that the decrease in electrical activity is due to deep levels resulting possibly from Al-Be related defects. An ordered structure and a compositional modulated structure were first observed in Ga0.5In0.5P grown by GSMBE. The degree of ordering was found to be less perfect than that for metalorganic vapor phase epitaxy (MOVPE) due to the lower growth temperature. Typical 300 K PL energy was found to be 1.88 eV which was 20 meV lower than the “normal” energy (1.9 eV).

GaxIn1−xP/GaAs grown by gas source molecular beam epitaxy using phosphine

Abstract Crystal properties of Ga x In 1− x P grown by gas source molecular beam epitaxy using phosphine (PH 3 ) were studied by using double crystal X-ray diffractmetry, Nomarski microscopy and photoluminescence (PL). Smooth surfaces were obtained if the lattice mismatch (Δ d / d ) ⊥ was less than about 5x10 −3 . The full width at half maximum of the PL spectra measured at 300 K was as narrow as 37.3 meV. The radial variations in layer thickness, PL intensity and composition are less than 10%, nearly constant and about 0.4%, respectively, across a 50 mm diameter wafer.

First 0.18 μm SBT-Based Embedded FeRAM Technology with Hydrogen Damage Free Stacked Cell Structure

An SBT-based embedded FeRAM has been successfully developed for the first time, which has been fabricated by using the 0.18 μm CMOS multi-level metal logic process. The highly-reliable FeRAM characteristics have been attained by the newly developed stacked cell structure which is fully enveloped by the top and bottom hydrogen barriers, resulting in the elimination of the hydrogen damage of the 0.18 μm multilevel metal process. The developed 0.18 μm SBT-based embedded FeRAM technology is most promising for commercialization of 0.18 μm embedded FeRAM and beyond.

A read-disturb-free ferroelectric gate fet memory

Abstract The enhancement-type ferroelectric gate field-effect transistor (FeFET) requires a read biasing voltage to the gate to secure a sufficient on/off current ratio. However, disturb (depolarization) of the ferroelectric by repetitive applications of read biasing voltage to the gate is a potential reliability concern. This paper deals with the disturb issue for an experimentally fabricated FeFET with a stacked gate comprised of metal/SrBi2Ta2O9/CeO2. A significant difference between a high ON current and a low OFF current is brought about and sustained after a large number of read operations by choosing a proper gate voltage, which is not only enough to make a positively programmed FeFET turn on, but also effective to prevent the disturb effect.

Mod preparation and characterization of blt thin film

Abstract The bismuth layered perovskite structured ferroelectrics (BLSF) are well known for their good ferroelectric characteristics. Recently, SrBi2Ta2O9 (SBT) and SrBi2Ta2-xNbxO9 (SBTN) have shown attractive properties for ferroelectric random access memories because of their high endurance characteristic. In addition to SBT and SBTN, their lies a possibility of many different BLSF materials waiting to be explored. One such material is lanthanum substituted bismuth titanate Bi4-xLaxTi3O12 (BLT) that has received some attention lately. The BLT thin films were prepared by conventional metal organic decomposition technique on the platinum electrode for evaluating ferroelectric characteristics of BLT and possibility of low temperature crystallization. It was found that BLT can be crystallized at 550C with random orientation and very good ferroelectric properties were observed: the remnant polarization (2Pr) was over 20μC/cm2 with low leakage current. Furthermore, the BLT capacitor did not show any significant fatigue up to 3.2×1010 cycles even at 85C.

Controlled metal-organic chemical vapor deposition of ferroelectric thin films

The metal-organic chemical vapor deposition (MOCVD) of ferroelectric thin films is being widely investigated for the manufacture of devices requiring both volatile and non-volatile memory. The consistent deposition of multicomponent thin films with uniform characteristics requires superior hardware engineering to control a large number of variables. Well known for its success in engineering III-V multicomponent thin film reactors, AIXTRON has combined liquid delivery system and showerhead designs with its established knowledge of temperature and pressure control for the deposition of strontium bismuth tantalate (SBT) and other ferroelectric chemistries. Among the important aspects of SBT MOCVD to be studied are the control of Sr and Ta incorporation and conformal coverage. Data on these two aspects of SBT thin film deposition are reported here.