Thin Films For MEMS Applications Research Articles

Influence of nano-clay platelet concentration on achieving a transition from write once read many (WORM) to complementary resistive switching (CRS) behaviour in organo-clay hybrid thin films for memory applications

Influence of nano-clay platelet concentration on achieving a transition from write once read many (WORM) to complementary resistive switching (CRS) behaviour in organo-clay hybrid thin films for memory applications

Recent advances in covalent organic polymers‐based thin films as memory devices

AbstractCovalent organic polymers (COPs) have emerged as a promising class of materials for memory devices due to their unique electronic properties and potential for tunability. This review highlights recent advances in the field of COPs‐based thin films for memory applications, with a focus on the synthesis and characterization of COP thin films, their electronic properties, and their performance as memory devices. The potential of COPs‐based thin films as flexible memory devices is also discussed. Overall, the recent progress in COPs‐based thin films for memory applications suggests that these materials may have a significant impact on the development of next‐generation memory technologies.

AFM Nanotribomechanical Characterization of Thin Films for MEMS Applications.

Nanotribological studies of thin films are needed to develop a fundamental understanding of the phenomena that occur to the interface surfaces that come in contact at the micro and nanoscale and to study the interfacial phenomena that occur in microelectromechanical systems (MEMS/NEMS) and other applications. Atomic force microscopy (AFM) has been shown to be an instrument capable of investigating the nanomechanical behavior of many surfaces, including thin films. The measurements of tribo-mechanical behavior for MEMS materials are essential when it comes to designing and evaluating MEMS devices. A great deal of research has been conducted to evaluate the efficiency and reliability of different measurements methods for mechanical properties of MEMS material; nevertheless, the technologies regarding manufacturing and testing MEMS materials are not fully developed. The objectivesof this study are to focus on the review of the mechanical and tribological advantages of thin film and to highlight the experimental results of some thin films to obtain quantitative analyses, the elastic/plastic response and the nanotribological behavior. The slight fluctuation of the results for common thin-film materials is most likely due to the lack of international standardization for MEMS materials and for the methods used to measure their properties.

Phenomenology of electrical switching behavior of SeTeSnCd thin films for memory applications

The objective of the present research is to investigate the consequences of the incorporation of a small amount of Cd on the electrical switching behavior at high electric field 104 V/cm in Se78-xTe20Sn2Cdx (x = 0, 2, 4, and 6) thin films. The thermal evaporation method has been utilized for thin-film deposition on a highly polished pyrographite substrate. The current-voltage (I-V) characteristics for the thin films of the examined samples exhibit a resistive switching of memory-type. The effect of ambient temperature and Cadmium content on the switching characteristics and voltage has been studied. The exponential decay in the observed average value of the switching voltage (Vth) is found with the rise in temperature and Cd addition as well. An endeavor had been done to study the observed compositional dependence in terms of the thermal-induced glass transition temperature (Tg), thermal stability, chemical bond approach, and lone-pair electrons (LP). On metal addition (Cd), the threshold voltage, glass transition temperature, and lone-pair electrons decrease while the chemical order network increases by the increase of the Cd-Se homopolar bonds. The switching phenomenon in amorphous Se78-xTe20Sn2Cdx (0 ≤ x ≤ 6) thin films is elucidated according to an electro-thermal model based on the Joule-heating effect.

Review and perspective on ferroelectric HfO2-based thin films for memory applications

Abstract

Ultra-smooth e-beam evaporated amorphous silicon thin films – A viable alternative for PECVD amorphous silicon thin films for MEMS applications

In this paper, we demonstrate the applicability of ultra-smooth e-beam evaporated amorphous silicon thin films (<500nm) as an alternative for PECVD thin films in MEMS applications. In this regard, a thorough investigation of the material and structural characteristics of low-temperature e-beam evaporated amorphous silicon thin films is carried out and it reveals that these properties are very similar to that of PECVD silicon thin films. E-beam evaporated amorphous silicon offers an ultra-smooth surface, which helps in realizing MEMS devices with close to ideal frequency response. The suitability of these thin films for MEMS applications is demonstrated by fabricating micro-cantilevers using the optimized thin film deposition conditions.

Pulsed laser deposition of SmCo thin films for MEMS applications

Thin films and coatings of permanent magnetic materials have found extensive applications in a wide range of technological domains. SmCo thin films show tremendous potential for use as permanent magnetic films on account of their high anisotropy fields, moderately high saturation magnetization and high curie temperature. In the present research, SmCo thin films have been deposited on single crystal Si(1 0 0) substrates using pulsed laser deposition technique. The films were deposited at a fixed substrate temperature of 400◦C by varying the number of pulses, in order to get thin films of different thicknesses. Effect of laser pulses on the crystal structure evolution, composition of the deposited material, film thicknesses and hence the magnetic properties have been investigated. X-ray diffraction analysis was performed in order to determine the crystal structure of the deposited films. The compositional analysis was performed by using energy dispersive X-ray spectroscopy. A slight variation in the Sm and Co contents was observed in the thin films grown by varying the laser shots. The microstructural information of the thin films was obtained by using a scanning electron microscope. The magnetic and electrical parameters were investigated by using vibrating sample magnetometer and two point probe respectively. The results show hard magnetic and conducting nature of all deposited thin films except sample 1 due to poor crystallinity.

Research on the Piezoelectric Properties of AlN Thin Films for MEMS Applications

In this paper, the piezoelectric coefficient d33 of AlN thin films for MEMS applications was studied by the piezoresponse force microscopy (PFM) measurement and finite element method (FEM) simulation. Both the sample without a top electrode and another with a top electrode were measured by PFM to characterize the piezoelectric property effectively. To obtain the numerical solution, an equivalent model of the PFM measurement system was established based on theoretical analysis. The simulation results for two samples revealed the effective measurement value d33-test should be smaller than the intrinsic value d33 due to the clamping effect of the substrate and non-ideal electric field distribution. Their influences to the measurement results were studied systematically. By comparing the experimental results with the simulation results, an experimental model linking the actual piezoelectric coefficient d33 with the measurement results d33-test was given under this testing configuration. A novel and effective approach was presented to eliminate the influences of substrate clamping and non-ideal electric field distribution and extract the actual value d33 of AlN thin films.

Substrate Influence on the Mechanical and Tribological Characteristics of Gold Thin Films for MEMS Applications

The development of micro-and nanoelectromechanical systems (MEMS/NEMS) makes use of different thin films such as aluminum, gold, silicon, silver, titanium nitride, silicon carbide etc. This study is a research concerning the influence of substrate nature on the tribological and mechanical characteristics of gold thin films elaborated by thermal evaporation method, for space applications. Three different substrates were employed, namely: C45 steel, plastic (polycarbonate) and glass. Atomic force microscopy investigations were performed in order to characterize the obtained thin films at nanoscale. The nanohardness, Young’s modulus, roughness and the friction force are some characteristics that were determined. A significant influence of substrate nature on both mechanical and tribological properties of researched gold thin films was marked out. Regarding the topography, the smallest roughness was determined on the gold thin films deposited on glass substrate.

Synthesis and Characterization of LPCVD Polysilicon and Silicon Nitride Thin Films for MEMS Applications

Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated MEMS devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not very well controlled during deposition. The residual stress, for example, tends to vary significantly for different deposition conditions; experiments were carried out to study the polysilicon and silicon nitride deposited by Low Pressure Chemical Vapor Deposition (LPCVD) method at wide range of process conditions. High temperature annealing effects on stress in case polysilicon are also reported. The reduced residual stress levels can significantly improve device performance, reliability, and yield as MEMS devices become smaller.

Identification of current transport mechanism in Al2O3 thin films for memory applications

The effect of oxygen anneal on the electrical characteristics, especially on the current transport mechanism, of Al2O3 films in the thickness range of 10–30 nm was examined in detail. The analyses were performed at electric fields of ≤2.5 MV/cm to effectively address the reliability of Al2O3-based devices operating in the low electric field regime. The general conduction mechanism equations were used to simulate the expected current density (J) values for a given electric field (E) range. The characteristic linear plots of the conduction mechanisms were then used to compare the experimental and simulated data to identify the most probable mechanism occurring in the dielectric. Parameters like barrier height and activation energy were extracted from the fit. It was found that oxygen anneal has profound effects on the electrical properties of Al2O3 films, with annealed films demonstrating a different conduction mechanism than their unannealed counterparts, along with significant improvement in the leakage current and barrier height. This kind of analyses will help optimize the process conditions for Al2O3 deposition and provide an optimal range for device operation, thus improving the reliability of Al2O3 films for applications in CMOS logic and Flash memory.

Programmable metallization cells based on amorphous La0.79Sr0.21MnO3 thin films for memory applications

Abstract We demonstrated a new programmable metallization cell based on amorphous La0.79Sr0.21MnO3 (a-LSMO) thin films for nonvolatile memory applications. The a-LSMO thin films were deposited on Pt/Ti/SiO2/Si substrates at 150 °C by radio frequency magnetron sputtering. The Ag/a-LSMO/Pt cell exhibited reversible bipolar resistive switching over 100 cycles with resistance ratio over 102 and stable retention for over 104 s. The impedance spectroscopy was used to analyze the conduction mechanism, and the resistive switching phenomena can be explained by the formation/rupture of Ag filaments in a-LSMO thin films utilized as solid electrolytes.

Printing of uniform PZT thin films for MEMS applications

A flexible manufacturing method for the deposition of lead zirconate titanate (PZT) thin films based on ink jet printing has been developed and used to fabricate a first functioning piezoelectric micromachined transducer by printing. The performance of the printed PZT based transducer was fit to established models to determine piezoelectric coupling and dielectric properties. The piezoelectric coefficient, d31, for printed PZT was between −75pC/N and −95pC/N. The relative permittivity was 750–890 and the dielectric loss tangent was 2.4–2.8%. This process enables digital deposition of printed devices with the key properties within the range required for high performance piezoelectric MEMS.

Recent advances in ferroelectric polymer thin films for memory applications

An overview of ferroelectric VDF/TrFE copolymer thin films is presented based on our recent work on their phase transition behavior and polarization switching dynamics. These properties originate in the hierarchical structures consisting of monomer dipoles, all-trans conformation, parallel chain packing and crystalline orientation in thin films. Successive loss of intermolecular and intramolecular orders yields multiple phase transitions from a ferroelectric phase to a molten phase via anti-ferroelectric and paraelectric phases. Polarization switching dynamics are shown to depend on a variety of factors not only applied field strength but also electrode, substrate, thickness and wave form of applied field. These results are discussed in relation to their hierarchical structures as well as nonvolatile memory applications.

Piezoelectric thin films for MEMS applications—A comparative study of PZT, 0.7PMN–0.3PT and 0.9PMN–0.1PT thin films grown on Si by r.f. magnetron sputtering

PMN–PT (0.7), PMN–PT (0.9) and PZT (54/46) thin films were deposited by sputtering on silicon substrate covered bottom TiO x /Pt electrodes. The top and lower electrodes are grown by r.f. sputtering. The objective in this paper here is to compare the dielectric, ferroelectric and piezoelectric properties of different materials, and material compositions, in thin films form. For these films the electric, ferroelectric and piezoelectric properties have been determined and compared to PZT films of the same thickness. The comprehensive characterization process clearly reveals the merits of each film composition for a particular application. The results for the three film compositions are presented and discussed.

Inorganic and Organic Ferroelectric Thin Films for Memory Applications

Electrical properties of inorganic and organic ferroelectric thin films are discussed from viewpoints of ferroelectric random access memory (FeRAM) applications. It has been found in BiFeO3 films formed by chemical solution deposition that the leakage current at high electric field decreases significantly by substituting Mn atoms for Fe atoms. In these films, well saturated hysteresis loops in P-E (polarization vs. electric field) characteristics have been observed. It has also been found that co-substitution of La and Ni atoms to BiFeO3 films is effective to decrease the leakage current. Next, properties of organic ferroelectric thin films suitable for fabricating ferroelectric-gate FETs (field effect transistors) are discussed. It has been found in capacitors with a 60nm-thick P(VDF+TrFE) (polyvinyliden fluoride-trifluoroethylene) film that the remanent polarization is as large as 11.9 μC/cm2 and the coercive voltage is as low as 2 V.

Inorganic and Organic Ferroelectric Thin Films for Memory Applications

not Available.

An investigation into which factors control the nanotribological behaviour of thin sputtered carbon films

Ultra-thin (20–100 nm) films deposited on Si surfaces can improve their mechanical and tribological properties. As a stepping stone towards the optimization of such ultra-thin films, herein we report experimental nanoscratch and nanowear data on a-C films of thickness in the range 200–1000 nm on Si aiming to (1) understand the role of film thickness on the nanoscratch behaviour, (2) determine whether the same factors (substrate bias, H/E ratio, etc) are at play for thick films as for the thin films, (3) determine possible design rules for thinner films enabling their optimization for MEMS applications and (4) evaluate the use of the multi-pass (3-scan) procedure for clarifying the locus of failure. To a first approximation, the critical load for total film failure in the nanoscratch test is proportional to thickness provided the films are not too stressed. a-C films of 1 µm with very high H/E, deposited under high substrate bias, perform well at low load but very poorly in more highly loaded situations. Not only do they exhibit low critical loads but also failure involves extensive delamination outside of the scratch track. This is not observed on thinner films. A suitable strategy for optimizing wear resistance for thin films for MEMS applications is to aim to maximize H/E. For the 200 nm films studied here, the films with the highest H/E showed slightly improved scratch resistance.

Mechanical cross-characterization of sputtered inconel thin films for MEMS applications

The characterization of Young's modulus, Poisson's ratio, linear coefficient of thermal expansion and residual stress of thin films is a critical issue for the design and development of MEMS. As inconel thin films have a relatively large thermal expansion coefficient together with a high electrical resistivity, they are good candidates for thermal actuators in MEMS. This work focuses on the determination of the mechanical properties of inconel thin films ranging from 0.4 up to 1.2 μm sputtered on a (100) silicon substrate. The atomic composition (6% Fe, 80% Ni, 14% Cr) of these films, close to that of inconel 600 alloys, has been determined by XRF analysis. A wafer curvature measurement technique is used to determine the residual stress and the linear thermal expansion coefficient. We measure residual stress between 152 and 342 MPa. The value of the linear thermal expansion coefficient is discussed but is found to be around 10 ppm/K −1. We perform bulge testing on micro machined square membranes to determine together the Young's modulus and residual stress of 0.4 μm films. Values of 166 GPa and 296 MPa are obtained, respectively. These results obtained by bulge testing are eventually compared with measurements made by nanoindentation. Good correspondence is found between the different methods.

Layer-by-layer self-assembled conductive thin films for MEMS applications

A layer-by-layer self-assembly process is investigated based on the alternate deposition of polyanion and polycation polymer materials onto oxidized silicon substrates for anti-static and electrical applications in MEMS devices. The polyanion and polycation in this study are sulfonated polystyrene and polypyrrole, respectively. The influence of FeCl 3 oxidant concentration is examined. It is found that the films prepared with higher oxidant concentrations exhibit lower resistivity; films prepared at 30 mM FeCl 3 show a resistivity of 0.05 Ω cm while those prepared at 6 mM FeCl 3 have values on the order of 0.15 Ω cm. The influence of doping with p-toluene sulfonic acid on the resistivity is found to be quite small, although the use of the dopant remains highly desirable for increased structural and thermal stability. Using atomic and electric force microscopy, the film morphology is found to exhibit nodular structures with an approximate grain size of 28 nm and 60 mV surface potential distribution. Finally, through reaction with octadecyl-sulfate sodium, the water contact angle of the pyrrole films have been shown to increase from 46° to 85°.