Films For Memory Applications Research Articles

Effect of oxygen-doping concentration on electrical properties of silicon oxycarbide films for memory application

We first investigate the effect of oxygen-doping concentration on resistive switching (RS) behaviors in SiCxOy, which were prepared by a radio frequency magnetron sputtering at the oxygen partial pressure ranging from 0% to 6%. Bipolar RS behaviors were achieved in all the fabricated devices and all these devices are valence change memories. With the oxygen partial pressure increasing from 0% to 6% (sample-0% has 40 at. % of oxygen), the mean RHRS increases from 4.5 to 64.8 MΩ and then decreases to 1.5 MΩ, indicating that the device exhibits the largest ON/OFF ratio ∼500 at the oxygen partial pressure of about 2%. Based on the analyses of x-ray photoelectron spectroscopy, fitting current–voltage curves, and resistance–temperature measurements, it is clear that the trap filled limit space charge limited current and a Schottky barrier in the interface of the SiCxOy film and p+-Si are suggested to be dominant in the positive and negative biases, respectively. Most importantly, all devices can keep the data more than 104 s and endure more than 102 continuous cycles, thus confirming the nonvolatile properties.

Structural influence of copper substrate on magnetic properties of electrodeposited CoPtP films for MEMS applications

Hard magnetic CoPtP films for MEMS application were electrodeposited on the various structures of copper substrate such as copper foil, copper seed layer and nano porous copper layer. The structural influence of copper substrates provided a reasonable explanation for the correlation of the magnetic properties of electrodeposited CoPtP alloy, because magneto-crystalline anisotropy could account for the enhancement of the perpendicular magnetic properties (Coercivity in highest range is achieved from 9.1 to 14.9 KOe) of the films. Also the influence of deposition current density on the chemical composition that changes the growth morphology, microstructure, and magnetic properties are studied.

Characterizations of evaporated α-Si thin films for MEMS application

Amorphous silicon (α-Si) thin films are widely used as electrical, optical and mechanical materials mainly synthesized by chemical vapor deposition (CVD) methods such as plasma-enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition. However, the physical vapor deposition ways which are seldom studied may demonstrate a proper choice for the deposition of α-Si thin films as the structural material for micro-electromechanical systems application. One of the CVD methods of e-beam thermal evaporation was used for the deposition of α-Si thin films in this study. All samples of deposited α-Si thin films had smooth surface with the root mean square surface roughness less than 1.6 nm. The α-Si film with a relatively low stress of about 250 MPa was obtained with a film thickness of 500 nm at a deposition rate of 4.7−6.1 A/s. The film thickness variation of α-Si deposited on a 4 inch white glass had a 0.78 % uniformity. The 150-nm-thick α-Si film showed a good conformality on the patterned 500-nm-thick Mo film and it had a leak current density of 2.8 × 10−3 A/cm2 under a 5 V bias voltage. The film’s Young’s modulus and hardness were extracted by a nano-indenter with values of 71.6 and 7.9 GPa, respectively. Characteristics of evaporated α-Si films and PECVD α-Si:H films were also compared.

Effects of the structural layer in MEMS substrates on mechanical and electrical properties of Pb(Zr 0.52Ti 0.48)O 3 films

In this paper, we describe the effects of the structural layer in substrates on the mechanical and electrical properties of Pb(Zr 0.52Ti 0.48)O 3 (PZT) films for MEMS applications. The PZT films were deposited by a sol–gel method on platinized silicon substrates where silicon nitride and silicon oxide were used as a structural layer. The mechanical properties of PZT films were characterized by nanoindentation. The ferroelectric and dielectric properties as a function of film thickness and layer material were investigated. Residual stresses in PZT films were also characterized by Raman spectroscopy. The measured mechanical properties of PZT films on two types of substrate indicate that the structural layer has significant influence on the obtained indentation moduli of PZT films. The PZT on SiN x -based substrates, i.e., PZT//SiN x /Si multilayer structure presented higher measured values than those of PZT on SiO 2-based substrate, i.e., PZT//SiO 2/Si multilayer structure throughout the whole indentation depth. The substrate effect on film hardness, however, was negligible since hardness value of around 8.8 GPa was measured for both PZT on SiN x and SiO 2-based substrates. Significant influences of the film thickness and substrate type on the electrical properties were not observed for the investigated thickness range of the PZT films.

Measurement of mechanical and thermal properties of co-sputtered WSi thin film for MEMS applications

In this study, mechanical and thermal properties of the co-sputtered tungsten silicide (WSi) thin film were evaluated to consider the possibility of its use in MEMS applications. WSi film was prepared by co-sputtering and basic micromachining processes, and its mechanical and thermal properties such as Young’s modulus, temperature coefficient of resistance (TCR), strain gauge factor, coefficient of thermal expansion (CTE) and thermal stress were studied. The measurement method was simple and efficient since only one test pattern was used for all measurements. At room temperature, the TCR, gauge factor, CTE and thermal stress were measured to be −670 ppm/°C, 2.8, 32 ppm/°C and 1.76 GPa, respectively. The dependence of these coefficients on temperature was also evaluated experimentally.

Diamond and Related Nanomaterials for MEMS/NEMS Applications

Diamond materials offer great potential for electronic and biomedical application. Properties like very high stiffness, thermal conductivity, optical transparency range, chemical stability and erosion resistance for the diamond based materials extend their applicability for several aspects of science and technology. Nanostructures of diamond materials have extraordinary multifunctional properties such as high thermal conductivity and a Youngs modulus value close to the one for single crystal diamond. Controlled nucleation and growth of nanocrystalline diamond along with their applicability for MEMS and NEMS structures are useful of future generation sensor platforms. Researchers around the world have been putting their efforts to achieve high precision in the direction of fabricating the devices based on diamond materials. Nanomanufacturing of such devices requires the controlled design of nanoscale diamond structures. This issue covers various topics related to carbon-based nanomaterials. The first article by Hanada et al. reports deposition process of ultrananocrystalline diamond films. Authors have demonstrated application of pulse laser deposition for diamond growth. The second article (by Ohmagari et al.) in this issue is about atomic bonding configuration of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C: H) films, where authors have used near-edge X-ray absorption fine structure spectroscopy. The third article (by Teng et al.) is about structural transformation upon nitrogen doping of ultrananocrystalline diamond films. Tanaka et al. report high-resolutionmagnetic force microscopy using carbon nanotube probes in the fourth article of this issue. In the fifth article, Tung et al. report fabrication of carbon nanotubes STM tips by liquid catalyst-assisted microwave plasma-enhanced chemical vapor deposition. In a similar type of study, Sakamoto et al. (the sixth article) report fabrication of Pd-filled carbon nanotubes for SPM applications. In the seventh article (by Katzenmeyer et al.), the authors report Poly (hydridocarbyne) as highly processable insulating polymer precursor to micro/nanostructures and graphite conductors. In the concluding article, I. Chasiotis and K. N. Jonnalagadda report strength and fracture resistance of amorphous diamond-like carbon films for MEMS applications.

A micrometer scale and low temperature PZT thick film MEMS process utilizing an aerosol deposition method

An aerosol deposition method and its lift-off process have been integrated for fabricating thick lead–zirconate–titanate (PZT) films for MEMS applications. The thickness of the deposited PZT films can be controlled over a wide range from 2 μm to more than 18 μm. In an area of 60 mm × 70 mm, an optimum deposition rate of 5 μm/h has been observed. For 13 μm thick PZT films, the minimum linewidth of 30 μm has been achieved. The fabricated thick PZT films exhibit a strong perovskite phase, after aerosol deposition at room temperature. To verify the functionality of deposited PZT films, a 7 μm × 700 μm × 900 μm cantilever-beam resonator has been fabricated. The resonance frequencies of the PZT cantilever resonator were measured and found to be similar to results of the finite element simulation. Finally, a functional 5 μm × 650 μm × 1200 μm PZT cantilever resonator was realized by annealing the PZT film at 500 °C.

Deposition of CoPtP films from citric electrolyte

Magnetically hard CoPtP (up to 40 μm thickness) films for MEMS application were deposited from citrate electrolyte and considered in terms of their composition, structure, magnetic characteristics and deposition conditions. Films containing 83–92 at.% (a/o) Co were deposited in the presence of NaH 2PO 2 in the electrolyte, with current efficiency of about 20% (deposition rate 10–12 μm/h). Coercivity 2.7–2.8 kOe and remanence 3.0 kG were achieved magnetizing in the direction normal to the film plane. According to XRD analysis, films seem to consist of hexagonal phase of CoPt solid solutions. Current efficiency, composition and morphology of the films, as well as their magnetic characteristics, were influenced by the electrolyte prehistory and total charge passed through the electrolyte in previous operation.

Remarkable Resistance Change in Plasma OxidizedTiOx/TiNx Film for Memory Application

We report the experimental phenomenon of large resistance change inplasma oxidized TiOx/TiNx film fabricated on Wbottom-electrode-contact (W-BEC) array. The W-BEC in diameter 260 nm isfabricated by a 0.18 μm CMOS technology, and theTiOx/TiNx cell array is formed by rf magnetron sputteringand reactive ion etching. In current–voltage (I–V) measurementfor current-sweeping mode, large snap-back of voltage is observed,which indicates that the sample changes from high-resistance state(HRS) to low-resistance state (LRS). In the I–V measurement forvoltage-sweeping mode, large current collapse is observed, whichindicates that the sample changes from LRS to HRS. The currentdifference between HRS and LRS is about two orders. The thresholdcurrent and voltage for the resistance change is about 5.0×10−5 A and 2.5 V, respectively. The pulse voltage can also changethe resistance and the pulse time is as shorter as 30 ns for theresistance change. These properties of TiOx/TiNx film arecomparable to that of conventional phase-change material, which makes itpossible for RRAM application.

POLYMER-ASSISTED MOD PREPARATION OF PbZr0.52Ti0.48O3 THICK FILMS FOR MEMS APPLICATIONS

ABSTRACT PbZr0.52Ti0.48O3 (PZT) (52/48) thick films with thickness between 1–5 μ m have been prepared by a metallo-organic decomposition process modified by polymer, poly(vinyl acetate) (PVAc). It has been found that PVAc can increase the single-layer thickness of PZT films. The PZT films with a single-layer thickness over 0.3 μ m have been obtained. The crack-free PZT films annealed at 650–700°C for 3 min exhibit a pure perovskite phase and good electrical properties with dielectric constant between 800–1200, dielectric loss less than 5%, remnant polarization around 28 μ C/cm2 and coercive field less than 100 kV/cm. PZT thick films prepared in this study are promising materials for MEMS applications.

Characterization of Low Stress, Undoped LPCVD Polycrystalline SiC Films for MEMS Applications

This paper details the characterization of polycrystalline SiC (poly-SiC) thin films deposited by low pressure chemical vapor deposition. Films were deposited on both Si and SiO2- coated Si substrates using dichlorosilane (SiH2Cl2) and acetylene (C2H2) as precursor gases. Low residual tensile stress films were deposited at 900°C at a pressure of 2 Torr using SiH2Cl2 and C2H2 (5% in H2) flow rates of 35 sccm and 180 sccm, respectively. XRD analysis of these films indicated a (111) 3C-SiC orientation regardless of substrate material. Both resistivity (1.3 -cm) and residual stress gradient (17 MPa/μm) were found to be relatively low and decreased as the film thickness increased. Unintentional nitrogen doping is responsible for the low resistivity measurements and its concentration in the films was about 1.86 x 1016 cm-3. Poly-SiC films exhibiting near-zero residual tensile stress, low stress gradient and relatively low resistivity have favorable properties for design and fabrication of MEMS devices.

Development of PECVD SiC for MEMS Using 3MS as the Precursor

AbstractThis paper reports our effort to develop amorphous hydrogenated silicon carbide (a-SiC:H ) films specifically designed for MEMS applications using a semiconductor-grade organosilane known as trimethylsilane (3MS) as the precursor. In our work, the a-SiC:H films were deposited in a commercial PECVD system at a fixed temperature of 350˚C using 3MS diluted in helium (He). Films with thicknesses from ~ 100 nm to ~ 2μm, a typical range for MEMS applications, were deposited. Deposition parameters such RF power, deposition pressure, and 3MS-to-He ratio were explored to obtain films with low residual compressive stresses. Low temperature, post-deposition annealing at 450˚C was used to convert the as-deposited compressive residual stresses to moderate tensile stresses, which are desired for micromachined bridges, membranes and other anchored structures. Compositional analysis indicated that films with a Si-to-C ratio of 1 could be deposited under certain conditions. Mechanical properties such as Young's modulus and fracture strength were derived from the load-deflection behavior of micromachined freestanding membranes. Nanoindentation was used to verify the Young's modulus and determine the hardness. As expected, the films exhibit insulating properties with a relative dielectric constant at 3.90 for as-deposited films and 2.69 after annealing at 1100˚C, as determined from C-V measurements. Chemical inertness was tested in aqueous, corrosive solutions such as KOH and HNA. Prototype structures were fabricated using both surface micromachining and bulk micromachining techniques to demonstrate the potential of the a-SiC:H films for MEMS applications.

High Quality Silicon-Based AlN Thin Films for MEMS Application

ABSTRACTAluminum nitride is an attractive piezoelectric material for MEMS devices such as bulk acoustic wave (BAW) devices. (002)-oriented AlN films were deposited on Si, Al and Pt by reactive sputtering. Optimized AlN (002) peak reaches a full width at half maximum (FWHM) of 5.6°. Auger electron spectroscopy is used to analyze the oxygen contamination of films. To find the suitable electrode material for device application, the growth mechanism of AlN crystallites on different substrates is also discussed. Based on sputtered AlN films, the prototype of AlN thin film bulk acoustic resonator (TFBAR) was fabricated successfully.

Characterization of Polycrystalline SiC Thin Films for MEMS Applications using Surface Micromachined Devices

Characterization of Polycrystalline SiC Thin Films for MEMS Applications using Surface Micromachined Devices

Microstructure of thick polycrystalline silicon films for MEMS application

Thick polysilicon films (>0.5 μm) become increasingly attractive for MEMS applications. However, thicker films can experience greater variability in morphology and in surface roughness due to the longer deposition time. In this study, 3.0 μm thick polysilicon films were deposited on silicon wafers by the LPCVD process. Asperities were observed on the surface of the polysilicon films by SEM and AFM. TEM studies showed the co-existence of equiaxed fine grains and some discrete long columnar crystallites containing microtwins (fine laths) in the materials microstructure. The asperities on the surface are found to be the caps of the columnar grains that grow continuously out of the flat surface of the equiaxed grains. The effect of the film thickness on these asperities and the surface quality was discussed.

Preparation, Microstructure and Physical Characteristics of Ferroelectric Pb5Ge3O11 Thin Films for Memory Application

ABSTRACTWe report sol-gel process of Pb5Ge3O11 (PGO) as well as the microstructure and physical properties of ferroelectric PGO films for memory applications. The PGO sol was prepared from lead acetate hydrate, germanium isopropoxide, and di(ethylene glycol) ethyl ether. The reactions taking place during the sol-gel process were examined in detail. Diethanolamine (DEA) was added to help maintain the desired species ratio and prevent germanium oxide precipitation. The preferred orientation of the PGO thin films was well controlled by the heating and reflux procedures in the sol-gel preparation process. Additionally, to examine the impact of postdeposition processing, selected samples were oxygen annealed at temperatures ranging from 450–650°C. The samples were characterized with X-ray diffraction (XRD), non-contact (planview) atomic force microscopy (NC-AFM). The resulting data indicate that the microstructure and physical properties of PGO films depend strongly on the precursor preparation as well as the post deposition annealing temperature.

Fabrication of (100) Orientated PZT Thin Films for MEMS Applications

High quality silicon-based PZT thin films were prepared using an improved sol-gel process. PT thin film was adopted as the seeding layer. The fabrication technique and the growth mechanism of the PZT thin films crystallized with (100) preferred orientation were studied through changing the pre-annealing temperatures, the annealing temperatures and the thickness of the PT seeding layer. It was shown that the PZT thin films with the suitable seeding layer had a more highly (100) preferred orientation. The dielectric response and dielectric loss of the PZT thin films were also measured. In the radio-frequency (RF) region, the dielectric constant was about 150 and the dielectric loss was less than 0.01, respectively.

Antiferroelectric thin films for MEMs applications

Antiferroelectric compositions have many potential applications in energy conversion and microelectromechanical systems. Electric field induced phase transitions between ferroelectric and antiferroelectric phases were studied in antiferroelectric lead zirconate and modified lead zirconate titanate stannate family thin films for various smart system applications. Thin films of various antiferroelectric thin film compositions such as PbZrO3, Nb-and La-modified Lead Zirconate Titanate Stannate were processed by pulsed excimer laser ablation technique. Dielectric, hysteresis, pyroelectric and switching properties were studied in detail for a new generation of functional materials. A comparative study of functional properties is presented with these antiferroelectric compositions in comparison with the conventional ferroelectric compositions.

Pulsed-laser deposition of Ta-doped PZT ferroelectric films for memory applications using conductive oxide La 0.25 Sr 0.75 CoO 3 and SrRuO 3 electrodes

New methods for fabricating highly -oriented and complete -textured Pb(Ta0.05Zr0.48Ti0.47)O3 (PTZT) films on Pt/TiO2/SiO2/Si(001) substrates by pulsed-laser deposition have been developed using conductive oxide La0.25Sr0.75CoO3 and SrRuO3 electrodes. The -preferred orientated PTZT ferroelectric capacitor was not subjected to loss of its polarization after 1×1010 switching cycles at an applied voltage of 5 V and a frequency of 1 MHz, and the -textured PTZT film capacitor retains 94.7% of its polarization after 1.5×1010 switching cycles at 5 V and 50 kHz. The PTZT capacitors using these conductive oxide electrodes have low leakage current dominated by Schottky field emission mechanism.

The characterisation of PZT films of differing orientations for MEMS applications

In order to utilise PZT thin films for MEMS applications it is essential to optimise the d 31 coefficient in order to maximise actuation efficiency. The d 31 coefficient, which can be optimised by the poling process, should be different for films of different orientation. PZT thin films of <110>, <100> and <111> have been deposited onto platinised silicon, their d 31 coefficient measured and their effectiveness as microactuators compared and evaluated.