Optimization of Pb(Zr0.53,Ti0.47)O3 films for micropower generation using integrated cantilevers

Lead zirconate titanate, Pb(Zr_0.53,Ti_0.47)O₃ or PZT, thin films and integrated cantilevers have been fabricated for energy harvesting applications. The PZT films were deposited on PECVD SiO₂/Si substrates with a sol-gel derived ZrO₂ buffer layer. It is found that lead content in the starting solution and ramp rate during film crystallization are critical to achieving large-grained films on the ZrO₂ surface. The electrical properties of the PZT films were measured using metal-ferroelectric-metal and inter-digital electrode structures, and revealed substantial improvement in film properties by controlling the process conditions. Functional cantilevers are demonstrated using the optimized films with output of 1.4 V peak-to-peak at 1 kHz and 2.5 g.     

Characteristics of metal-ferroelectric-insulator-semiconductor structure using Sr0.8Bi2.2Ta2O9 and Sr0.8Bi2.2Ta2O9-BaZrO3 for ferroelectric gates

Characteristics of BaZrO₃ (BZO) modified Sr_0.8Bi_2.2Ta₂O₉ (SBT) thin films fabricated by sol-gel method on HfO₂ coated Si substrates have been investigated in a metal-ferroelectric-insulator-semiconductor (MFIS) structure for potential use in a ferroelectric field effect transistor (FeFET) type memory. MFIS structures consisting of pure SBT and doped with 5 and 7 mol% BZO exhibited memory windows of 0.81, 0.82 and 0.95 V with gate voltage sweeps between −5 and +5 V, respectively. Leakage current density levels of 10⁻⁸ A/cm² for BZO doped SBT gate materials were observed and attributed to the metallic Bi on the surface as well as intrinsic defects and a porous film microstructure. The higher than expected leakage current is attributed to electron trapping/de-trapping, which reduces the data retention time and memory window. Further process improvements are expected to enhance the electronic properties of doped SBT for FeFET.     

Electrical properties of metal-ferroelectric-insulator-semiconductor structure using BaxSr1−xTiO3 for ferroelectric-gate field effect transistor

Perovskite ferroelectric Ba_xSr_1−xTiO₃ (x = 0.5, 0.6, 0.7 and 0.8) thin films have been fabricated as metal-ferroelectric-insulator-semiconductor (MFIS) configurations using a sol-gel technique. The C-V characteristics for different Ba-Sr ratios and different film thicknesses have been measured in order to investigate the ferroelectric memory window effect. The results show that the memory window width increases with the increase both of Ba content and film thickness. This behavior is attributed to the grain size and dipole dynamics effect. It is found also that the memory window increases as the applied voltage increases. In addition, the leakage current density for the films is measured and it is found to be of the order of 10⁻⁸ A/cm² for all tested samples, indicating that the films have good insulating characteristics.     

Highly (1 0 0)-oriented Pb(Zr0.20Ti0.80)O3/(Pb1−xLax)Ti1−x/4O3 multilayered thin films prepared by RF magnetron sputtering

The Pb(Zr_0.20Ti_0.80)O₃/(Pb_1−xLa_x)Ti_1−x/4O₃ (x = 0, 0.10, 0.15, 0.20) (PZT/PLT_x) multilayered thin films were in situ deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering technique with a PbO_x buffer layer. With this method, all PZT/PLT_x multilayered thin films possess highly (1 0 0) orientation. The PbO_x buffer layer leads to the (1 0 0) orientation of the multilayered thin films. The effect of the La content in PLT_x layers on the dielectric and ferroelectric properties of the PZT multilayered thin films was systematically investigated. The enhanced dielectric and ferroelectric properties are observed in the PZT/PLT_x (x = 0.15) multilayered thin films. The dielectric constant reaches maximum value of 365 at 1 KHz for x = 0.15 with a low loss tangent of 0.0301. Along with enhanced dielectric properties, the multilayered thin films also exhibit large remnant polarization value of 2P_r = 76.5 μC/cm², and low coercive field of 2E_c = 238 KV/cm.     

Structural and electrical characteristics of RF-sputtered HfO2 high-k based MOS capacitors

The HfO₂ high-k thin films have been deposited on p-type (1 0 0) silicon wafer using RF magnetron sputtering technique. The XRD, AFM and Ellipsometric characterizations have been performed for crystal structure, surface morphology and thickness measurements respectively. The monoclinic structured, smooth surface HfO₂ thin films with 9.45 nm thickness have been used for Al/HfO₂/p-Si metal-oxide-semiconductor (MOS) structures fabrication. The fabricated Al/HfO2/Si structure have been used for extracting electrical properties viz dielectric constant, EOT, barrier height, doping concentration and interface trap density through capacitance voltage and current-voltage measurements. The dielectric constant, EOT, barrier height, effective charge carriers, interface trap density and leakage current density are determined are 22.47, 1.64 nm, 1.28 eV, 0.93 × 10¹⁰, 9.25 × 10¹¹ cm⁻² eV⁻¹ and 9.12 × 10⁻⁶ A/cm² respectively for annealed HfO₂ thin films.     

Properties of transparent conductive ZnO:Al thin films prepared by magnetron sputtering

Middle-frequency alternative magnetron sputtering was used to deposit transparent conductive ZAO (ZnO:Al) thin films with ZAO (98 wt%ZnO+2 wt%Al₂O₃) ceramic target on glass and Si wafers. The influences of the various deposition parameters on the structural, optical and electrical performances of ZAO films have been studied. The structural characteristics of the films were investigated by the X-ray diffractometer and atomic force microscope, while the visible transmittance, carrier concentration and Hall mobility were studied by UV-VIS and the Hall tester, respectively. The lowest resistivity obtained in the work was 4.6×10⁻⁴ Ω cm for the film with average transmittance of 90.0% within the visible wavelength range and sheet resistance of 32 Ω, which was deposited at 250 °C and 0.8 Pa.     

Study of electrical and optical properties of CNx thin films deposited by reactive magnetron sputtering

The study concerns the CN_x thin films deposited by Low Pressure Hot Target Reactive Magnetron Sputtering (LP-HTRMS). The thin film resistance changes with relative humidity (RH) and optical properties have been studied in the range of 300-653 K. The temperature coefficients of resistivity changes were −2.5%/K at 300 K and −0.5%/K at 500 K. The activation energy of conductivity E_ρ was found to be 0.21 eV in the case of unannealed sample and 0.44 eV when the sample was annealed at 653 K. The CN_x thin films fastness to light was tested in the range of 200-2500 nm by measuring their transmittance. The calculations of absorption carrying out with Tauc formula proved the dominance of indirect optical transitions with Eg energy of 1.04 eV and direct transitions of Eg 2.05 eV. The UV radiation was fully absorbed and light transmission was ca. 90% in the range from visible radiation to far infrared of 1000-2500 nm. The CN_x thin films showed the high resistance sensitivity to RH changes. At T = 300 K resistance changed from 882 M Ω for 36% RH to 386 k Ω for 85% RH. The CN_x thin films susceptibility to humidity was observed in case of both DC and AC current (100 Hz to 10 kHz) measurements. The Si₃N₄ or SiC buffer adhesive layer was incorporated between CN_x film and substrate and its influence on CN_x electrical properties was observed.     

Top injection reactor tool with in situ spectroscopic ellipsometry for growth and characterization of ALD thin films

Ta-N based thin films were grown by thermal atomic layer deposition (ALD) with an alternating supply of the reactant source TBTDET (tert-butylimidotris(diethylamido)tantalum) and NH₃ (ammonia). The films were deposited using a newly designed and constructed atomic layer deposition prototype tool combined with several in situ metrology. It was observed that thin films were successfully deposited on a 300 mm Wafer with a saturated growth rate of approximately 0.55 Å/cycle at 270 °C. The as deposited films resulted in the formation of Ta(C)N consisting of 38 at% Ta, 32 at% N and 10 at% C. With in situ spectroscopic ellipsometry (SE) the growing behaviour of the film was investigated and compared to atomic force microscopy (AFM) images.     

Li-doped (Ba,Sr)TiO3 thick film interdigital capacitors for microwave applications

Microwave properties of Li-doped (Ba,Sr)TiO₃ thick film interdigital capacitors have been investigated. According to the reported papers, BaSrTiO₃ materials, paraelectric state at the room temperature, have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (<0.01 @ 1 MHz) in epitaxial thin film form; however, the sintering temperature of BaSrTiO₃ is over 1350 °C. In order to reduce the sintering temperature, Li (3 wt%) was added to the BaSrTiO₃ materials, and 10 μm thick Li-doped (Ba,Sr)TiO₃ films were screen printed on the alumina (Al₂O₃) substrate and sintered at 900 °C. Interdigital capacitor patterns with five fingers of 200 μm gap and 250 μm length were also designed and fabricated by employing the screen printing method with Ag electrode. The structural feature was analyzed with X-ray diffraction method. Frequency and temperature-dependent dielectric properties were characterized from 1 kHz to 1 MHz and 303-403 K, respectively. Also, current-voltage characteristics were investigated with an elevated temperature. Microwave transmission and reflectance properties of thick film interdigital capacitors will be discussed, and frequency dispersion of dielectric properties will be presented. Specially, designed Au/Li-doped (Ba,Sr)TiO₃/Ag-Pd/Al₂O₃ vertical structure was prepared to measure the tunability. In this sandwich type structure, Li-doped (Ba,Sr)TiO₃ films showed tenability of 7.15% at a bias electric field of 20 kV/cm.     

The microwave properties of Li doped 0.7(Ba,Sr)TiO3-0.3MgO thick film interdigital capacitors on the alumina substrates

The crystalline and electrical properties of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick film interdigital capacitors have been investigated. Screen printing method was employed to fabricate Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films on the alumina substrates. (Ba,Sr)TiO₃ materials have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (0.01 @ 1 MHz) in the epitaxial thin film form. To improve dielectric properties and reduce sintering temperature, MgO and Li were added, respectively. 10 μm thick films were screen printed on the alumina substrates and then interdigital capacitors with seven fingers of 200 μm finger gap were patterned with Ag electrode. Current-voltage characteristics were analyzed with elevated temperature range. Up to 50 °C, the thick films showed positive temperature coefficient of resistivity (dρ/dT) of 6.11 × 10⁸ Ω cm/°C, then film showed negative temperature coefficient of resistivity (dρ/dT) of −1.74 × 10⁸ Ω cm/°C. From the microwave measurement, the relative dielectric permittivity of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films interdigital capacitors were between 313 at 1 GHz and 265 at 7 GHz.     

Characterization of UV photodetectors with MgxZn1−xO thin films

In this study the metal-semiconductor-metal (MSM) structure ultraviolet (UV) photodetectors (PDs) based on Mg_xZn_1−xO thin films were fabricated. The Mg_xZn_1−xO thin films were grown on glass substrates by sol-gel method. The results show that the optical absorption has a blue shift and higher transmittance with increasing Mg dopant. The optical band gap were modified by 3.28-3.52 eV, which corresponded to x = 0 and x = 0.16. For a 10 V applied bias, the dark currents of the Mg_xZn_1−xO MSM-PDs were 637 nA (x = 0) to 0.185 nA (x = 0.16) and showed good Schottky contacts. This UV-visible rejection ratio of the Mg_xZn_1−xO UV PDs at x = 0, 0.16, 0.21 and 0.33 were 18.82, 35.36, 40.91 and 42.92, respectively.     

Laser printing of air-stable high performing organic thin film transistors

Active layers involved in top contact organic thin film transistors (TC-OTFTs) have been printed using the laser induced forward transfer (LIFT) technique. Bis(2-phenylethynyl) end-substituted terthiophene (diPhAc-3T) as a p-type organic semiconductor was vacuum evaporated on a quartz substrate prior to the transfer by laser onto an acceptor substrate to form an organic active layer for charge transport. The resulting printed diPhAc-3T pixels on the receiver substrates have a homogeneous morphology as shown by optical microscopy and atomic force microscopy (AFM). Electrical characterizations demonstrated that these transistors are fully functional with hole mobilities up to 0.04 cm²/V s, threshold voltage V_t near 0 V and I_on/I_off ratio up to 2.8 × 10⁵. The efficient cohesion of diPhAc-3T vacuum evaporated thin films induced by 3-dimensional growth offers an exceptionally high physical resistance to laser pulses. The large intermolecular interaction involved in such growth mechanism makes the thin films less sensitive to the mechanical damages induced by the laser. Due to the optical properties of diPhAc-3T, the use of a protecting layer deposited on the donor substrate prior to the diPhAc-3T active layer to trap the incident radiation during the LIFT was not required.     

Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol-gel method and reaction-anneal treatment

Hafnium oxide (HfO₂) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl₄) source by surface sol-gel process, then ultrathin (HfO₂)_x(SiO₂)_1−x films were fabricated due to the reaction of SiO₂ layer with HfO₂ under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol-gel derived ultrathin films are Hf-Si-O alloy instead of HfO₂ and pre-grown SiO₂ layer, and the composition was Hf_0.52Si_0.48O₂ under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO₂)_x(SiO₂)_1−x composite films has been developed by means of combination of surface sol-gel and reaction-anneal treatment.     

Plasma etching of copper films at low temperature

Experimental verification of a low temperature (<20 °C), reactive plasma etch process for copper films is presented. The plasma etch process, proposed previously from a thermochemical analysis of the Cu-Cl-H system, is executed in two steps. In the first step, copper films are exposed to a Cl₂ plasma to preferentially form CuCl₂, which is volatilized as Cu₃Cl₃ by exposure to a H₂ plasma in the second step. Plasma etching of thin films (9 nm) and thicker films (400 nm) of copper has been performed; chemical composition of sample surfaces before and after etching has been determined by X-ray photoelectron and flame atomic absorption spectroscopies.     

Effect of oxygen partial pressure on conductivity type of MgZnO nanocrystalline thin films prepared by metal-organic chemical vapor deposition

The properties of the MgZnO nanocrystalline thin films deposited on c-Al₂O₃ substrates by metal-organic chemical vapor deposition (MOCVD) at various oxygen partial pressures (Po₂) were thoroughly studied. It was found that the nanocrystalline films grown in the oxygen partial pressure range from 38 to 56 Pa were all c-axis oriented. From the atomic force microscope (AFM) images and photoluminescence (PL) spectra, we could also find that both the surface morphologies and the optical properties of the MgZnO nanocrystalline thin films depended on the oxygen partial pressure greatly. Hall effect measurements confirmed the conversion of conduction type of MgZnO under a certain range of oxygen partial pressure. With the increase of oxygen content, the crystallinity of MgZnO nanocrystalline thin films was degraded to polycrystalline and the p-type MgZnO was produced when the oxygen partial pressure was larger than 50 Pa. The hole concentration and mobility could reach to 9.71×10¹⁷ cm⁻³ and 2.44 cm² V⁻¹ s⁻¹, and the resistivity was 2.87 Ω cm while the oxygen partial pressure was 56 Pa.     

H2 carrier gas dependence of Young's modulus and hardness of chemical vapor deposited polycrystalline 3C-SiC thin films

This paper presents the mechanical properties of poly (polycrystalline) 3C-SiC thin films according to 0%, 7%, and 10% carrier gas (H₂) concentrations using nano-indentation. When H₂ concentration was 10%, it has been proved that the mechanical properties, Young's modulus, and hardness of poly 3C-SiC films are the best of them. In the case of 10% H₂ concentration, Young's Modulus and hardness were obtained as 367 and 36 GPa, respectively. The surface roughness according to H₂ concentrations was investigated by AFM (atomic force microscope). When H₂ concentration was 10%, the roughness of 3C-SiC thins was 9.92 nm, which is also the best of them. Therefore, in order to apply poly 3C-SiC thin films to MEMS (micro-electromechanical system) applications, H₂ concentration's rate should increase to obtain better mechanical properties and surface roughness.     

Electromigration resistance and long term stability of textured silver thin films on LTCC

Silver (Ag) is regarded as advanced material for metallization purposes in microelectronic devices because of its high conductivity and its enhanced electromigration resistance. Besides the typical use of silicon based substrate materials for device fabrication, thin film metallization on ceramic and glass-ceramic LTCC (low temperature co-fired ceramics) substrates gets more and more into focus as only thin film technology can provide the required lateral resolutions of structures in the μm-range needed for e.g. high frequency applications. Therefore, the reliability of Ag thin films is investigated under accelerated aging conditions, utilizing test structure which consists of 5 parallel lines stressed with current densities up to 1.5 × 10⁷ A cm⁻² at temperatures ranging from room-temperature up to 300 °C. To detect the degradation via the temporal characteristics of the current signal a constant voltage is applied taking the overall resistance of the test structure into account. The mean time to failure of the Ag metallization substantially depends on the degree of (1 1 1)-orientation which, in turn, is strongly affected by the plasma power P_P during deposition. Therefore, Ag thin films deposited at P_P = 1000 W feature a 7 times higher reliability than those deposited at P_P = 100 W. Due to the enhanced stability of grains being (1 1 1)-oriented in textured thin films the material transport predominantly occurs along grain boundaries, whereas in Ag films without a (1 1 1)-orientation volume-related diffusion effects dominate due to the lower stability of these grains.     

Effect of Si/Ta and nitrogen ratios on the thermal stability of Ta-Si-N thin films

Ta-Si-N thin films were fabricated by using reactive magnetron cosputtering at different Si/Ta power ratios and nitrogen (N₂) to total gas (Ar + N₂) flow ratios (FN₂% = FN₂/(FAr + FN₂) × 100%). Both levels of high-vacuum furnace annealing (FA) and low vacuum rapid thermal annealing (RTA) were performed to investigate the thermal stability of films. The microstructure, morphology and electrical property of the Ta-Si-N thin films were characterized by grazing incidence X-ray diffraction, scanning electron microscope and four-point probe method, respectively. Ta-Si-N thin films at low FN₂% could endure temperature up to 900 °C for 1 h under high-vacuum FA at 6.5 × 10⁻³ Pa while their phase and morphology had changed under RTA at 750-900 °C for 1 min at 2.6 Pa. The resistivity increased with increasing both FN₂% and Si/Ta power ratios. However, the variation percentage of resistivity of Ta-Si-N films at high-temperature annealing decreased with increasing Si/Ta power ratio and inversely increased with increasing FN₂%. In brief, the thermal stability of Ta-Si-N films increased with increasing level of vacuum and Si/Ta power ratio. Increasing FN₂% and Si/Ta power ratio could enhance the thermal stability of films at RTA but also increased the resisitivity of films. Therefore, Ta-Si-N films prepared at 2 FN₂% and Si/Ta power ratio of 2/1 can be a good candidate for the application of diffusion barrier with low resistivity, low variation percentage and high stability of microstructure.     

Physical properties in thin films of iron oxides

We have grown hematite (α-Fe₂O₃) thin films on stainless steel substrates and magnetite (Fe₃O₄) thin films on (0 0 1)-Si single crystal substrates by a RF magnetron sputtering process. α-Fe₂O₃ thin films were grown in an Ar atmosphere at substrate temperatures around , and Fe₃O₄ thin films in an Ar/O₂ reactive atmosphere at substrate temperatures around . Conversion electron Mössbauer (CEM) spectra of α-Fe₂O₃ thin films exhibit values for hyperfine parameter characteristic of the hematite stoichiometric phase in the weak ferromagnetic state [R.E. Vandenberghe, in: Mössbauer Spectroscopy and Applications in Geology, University Gent, Belgium, 1990. [1]]. Furthermore, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The CEM spectra of Fe₃O₄ thin films show the presence of only the stoichiometric phase, and the values for the hyperfine fields and isomer shifts of the A and B sites are consistent with bulk Fe₃O₄[1]. The X-ray diffraction (XRD) pattern of the polycrystalline thin films also corresponds to α-Fe₂O₃ and Fe₃O₄ [JCPDS, X-ray diffraction data cards, 2001. [2]]. The samples were also analyzed by atomic force microscopy (AFM) and they reveal a grain morphology common for polycrystalline films. We found an average grain size of 211 nm and surface roughness of 45 nm in α-Fe₂O₃ films and an average grain size of 148 nm and surface roughness of 1.2 nm in Fe₃O₄ films.     

Electrical and reliability characteristics of GaAs MOSHEMTs utilizing high-k IIIB and IVB oxide layers

In this work, the high-k material of gadolinium oxide layer (Gd₂O₃) and zirconium oxide layer (ZrO₂) thin films were fabricated as the gate dielectric insulator materials in GaAs metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs). The dielectric constant of Gd₂O₃ and ZrO₂ oxide layers were estimated to be 10.6 and 7.3 by the MOS-ring capacitor of C-V measurements. In addition, the thermal stability of the devices have been investigated and compared with the high-k material Gd₂O₃ and ZrO₂ thin films for reliability tests. The Gd₂O₃ MOSHEMTs achieved a better thermally stable characteristic duo to its similar lattice structure with GaAs native oxide layer. At high temperature operation, the V_BR degradation slope was 1.2 × 10⁻³ V/°C and the maximum I_ds degradation slope was 1.4 × 10⁻² mA (%)/°C. According to this, the device also showed a good reliability characteristic within 48 h. Based on measurement results, the Gd₂O₃ MOSHEMTs exhibited the best electrical characteristics, including the lowest gate leakage current, the lowest noise spectra density, and the high power performance. Therefore, the Gd₂O₃ MOSHEMTs is suitable for high power amplifier and monolithic microwave integrated circuits (MMICs) applications.