Metalorganic chemical vapor deposition of ferroelectric Pb(Zr,Ti)O3 thin films

Abstract

The controllability of PZT film properties and the possibility of the scaling up the MOCVD to the commercial based production were briefly reviewed. The film composition and crystalline phase of the PZT films were easily controlled using the MOCVD process. The electrical properties were also controlled by changing the growth parameters. A low processing temperature was achieved using a new Pb precursor, tryethyl n-pentoxy lead. Large area growth of PZT and PLZT films on a 6–8 inch wafer was also achieved.     

Deposition and gas sensing properties of tin oxide thin films by inductively coupled plasma chemical vapor deposition

Tin oxide thin films have been deposited by a custom-designed inductively coupled plasma chemical vapor deposition (ICP-CVD) system in order to explore its application as an alternative approach for thin film gas sensor preparation. The as-deposited SnO₂ films were of polycrystalline structure with nano-size grains of 12 nm. The SnO₂ films exhibited a maximum sensitivity of 43 to 1000 ppm H₂ at an optimum operating temperature of 350^∘C. The response time of the SnO₂ films was 12 s and full recovery was achievable.     

PZT thick films by diol chemical solution deposition

Process optimization and properties of lead zirconate titanate (PZT) films for piezoelectric micromachined ultrasonic transducers (pMUTs) for scanning probe devices will be presented. The goal of the work was a replacement of the tetragenic and mutagenic solvent and a decrease of time-consuming PZT 2–methoxy ethanol (2MOE) route. An alternative diol-based solution synthesis process was developed and “Design Of Experiment” (DOE) was used to achieve processing optimization for thick and crack free films. Tight parameter control allowed to develop a highly reproducible PZT diol process. The crystallization behaviour of crack-free PbZr_0.53Ti_0.47O₃ films (1–5 μm) with oriented perovskite structure was examined by X-ray diffraction and surface analysis using scanning electron microscopy. Piezoelectric and dielectric properties were examined. The effective transverse piezoelectric coefficient e _31,f of sol–gel processed films was investigated for 4 μm thick layers. Best properties were achieved with {1 0 0}-textured films, where a remanent e _31,f value of −7.3 C/m² was measured for 4.1 μm thick films.     

Selective growth of InAs quantum dots by metalorganic chemical vapor deposition

We report results of both strain-driven surface segregation of indium from InGaAs thin films as well as selective area epitaxy of InAs quantum dots using these films. InAs segregation from an underlying InGaAs film allows for preferential growth of quantum dots when additional InAs is deposited. By using standard lithography techniques, a two-step selective growth process for quantum dots is achieved. Furthermore, by utilizing self-assembled nanostructures as a template, selective growth of coalesced wires and dots with 100-nm feature sizes are realized.     

Sputter deposition of ferroelectric thin films

Ferroelectric films are typically deposited by a variety of techniques, the two most common being chemical methods (sol-gel, metalorganic decomposition) and sputtering. In this paper we briefly review the sputtering techniques, and then discuss ion beam sputter deposition in greater detail. In particular, ion beam sputter deposition of epitaxial lead zirconate titanate (PZT) films is described. It is shown that the films with compositions close to the morphotropic boundary typically show well-developed ferroelectric hysteresis loops, Pmax around 45 μC/cm2, and Pr around 20 μC/cm2. In comparison with typical polycrystalline sol-gel PZT films, however, coercive fields of thin epitaxial films are large (120-200 kV/cm for 95 nm films). The pulsed fatigue behavior is remarkably similar to a polycrystalline non-oriented sol-gel PZT film investigated for comparison. The similarities suggest that the aging behavior may be dominated by the electrodes, which were Pt in both systems.     

4.2-mW GaInNAs long-wavelength VCSEL grown by metalorganic chemical vapor deposition

We achieved high output power GaInNAs vertical-cavity surface-emitting lasers (VCSELs) emitting at 1261.5 nm by means of decreasing the incorporation of aluminum into the GaInNAs well layers. The continuous wave (CW) output power at room temperature reached 4.2 mW, with a slope efficiency of 0.52 W/A. Secondary ion mass spectrometry (SIMS) analysis revealed that the aluminum incorporated into the GaInNAs layer did not originate from diffusion from the adjacent layers of GaInNAs, but from residual aluminum in the reactor.     

Preparation and characterization of PZT thin films deposited on PZT buffer layer with different lead content

Lead zirconate titanate (PZT) thin films deposited on Pt electrode and Pb_1+x(Zr_0.52,Ti_0.48)O₃ (x = 0.10, 0.15, 0.25, 0.30) buffer layer have been prepared by sol-gel methods to investigate the effects of lead content in the buffer layer on crystalline orientation, electric and fatigue properties of PZT films. XRD and SEM showed that all films exhibited dense perovskite structure with (100) preferential orientation. The maximum dielectric constant (1571 at 100 Hz) was obtained in the PZT film with buffer layer containing 25% excess lead, which increased by 42.5% compared with the film without buffer layer. Fatigue resistance was improved by introducing buffer layer.     

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.     

Recent progress in sputtering PZT thin films for ferroelectric memories

Abstract

This paper describes amorphous Pb(Zr, Ti)O₃ (PZT) thin films deposited by cosputtering Pb(Zr_0.5 Ti_0.5)O₃ and PbO targets. By optimizing the amount of the excess Pb and the deposition temperature, PZT thin films with a single perovskite phase were obtained successfully on Ir substrates and Pt substrates at 520°C. 250-nm-thick PZT films crystallized by rapid thermal annealing (RTA) at 600°C for 20 s exhibited excellent ferroelectric properties: a coercive voltage of 1.0 V, a remanent polarization density of about 40 μC/cm², and a polarization switching endurance over 1x109 cycles. Although a heat treatment in a reductive ambient causes degradation of ferroelectric properties of PZT thin films, their degraded ferroelectric properties can be easily recovered from by a 1-min RTA in an oxygen at 400°C.     

化学水浴法制备ZnS薄膜

采用了化学水浴法制备异质结薄膜太阳电池中的窗口层ZnS薄膜.尝试了酸性溶液制备ZnS薄膜,讨论了溶液成分、水浴时间和温度对薄膜成分和形貌的影响.研究结果表明在75℃,6 h条件下沉积得到的薄膜最平整,成分最符合化学计量比,退火后薄膜主要为纤锌矿结构的ZnS相.     

High-performance 1200-nm InGaAs and 1300-nm InGaAsN quantum-well lasers by metalorganic chemical vapor deposition

In this paper, we present the characteristics of high-performance strain-compensated MOCVD-grown 1200-nm InGaAs and 1300-nm InGaAsN quantum-well (QW) lasers using AsH/sub 3/ and U-Dimethylhydrazine as the group V precursors. The design of the InGaAsN QW active region utilizes an In-content of approximately 40%, which requires only approximately 0.5% N-content to realize emission wavelengths up to 1315-nm. Threshold current densities of only 65-90 A/cm/sup 2/ were realized for InGaAs QW lasers, with emission wavelength of 1170-1233 nm. Room-temperature threshold and transparency current densities of 210 and 75-80 A/cm/sup 2/, respectively, have been realized for InGaAsN QW lasers with emission wavelength of 1300-nm. Despite the utilization of the highly-strained InGaAsN QW, double-QW lasers have been realized with excellent lasing performance.     

Characterization of conduction in PZT thin films produced by laser ablation deposition

Abstract

Both direct current (d.c.) and alternating current (a.c.) conductivity measurements were undertaken on lead zirconate titanate (PZT) films synthesized by laser ablation deposition. Direct current (I) displayed an initial time dependence of the form I ∝ t^?γ (γ ∝ 0.5–1.0). The possible reasons for this time dependence are discussed. At lower temperatures, the a.c. electrical conductivity shows a frequency dependence of the form σ ∝ ω′ which is explained as electrical charge hopping. At higher temperatures, the d.c. component of electrical conductivity becomes dominant, and is accompanied by a strong low frequency dispersion of the dielectric constant. The results are compared to published data on conductivity in SrTiO₃, and discussed in terms of the latest theories for dielectric response of materials.     

Recent advances in the deposition of ferroelectric thin films

Abstract

Recent developments in ferroelectric thin film deposition involving plasma based approaches, are described, which include a) multi-magnetron sputter deposition, b) Multi-ion-beam reactive sputter (MIBERS) deposition, c) Pulsed excimer laser ablation and d) ECR (Electron cyclotron resonance) plasma assisted deposition. These methods commonly prevailed intrinsic low energy ion bombardment during the growth process, which may be used for the control over composition, crystallization temperature and microstructure. A low energy (60–75 eV) ion bombardment of the ferroelectric Pb(Zr, Ti)O₃ thin films indicated a reduction in the phase formation/crystallization temperature, improved the electrical properties, microstructure and the surface smoothness. Discussion is presented exphasizing the effects of low energy bombardment in different deposition processes. Recent findings using rapid thermal annealing process are also described.     

Development of ferroelectric PZT thin films by the sol-gel technique for non-volatile memory applications

Abstract

PZT thin films have been prepared via a sol-gel route using standard butoxide and acetate precursors. The solution compositions were modified by the addition of acetylacetone in 2 methoxyethanol, which has the effect of changing the solution complex and therefore its deposition and drying characteristics. Varying amounts of excess lead were included in some cases. The films were prepared by spin coating onto Pt/Ti electroded silicon with an intermediate barrier layer of either boron phosphate silica glass (BPSG) or thermal silicon oxide and the resulting samples subjected to a range of thermal annealing conditions in an oxidising atmosphere. Several methods have been investigated including two regimes using rapid furnace annealing (RFA) up to 700°C and slow annealing at 450°C in air. The latter method yielded highly (111) oriented and crack-free perovskite films with no evidence of other orientations, whereas the former route showed the presence of (100) and (110) orientations. The correlation between the thermal anneal method and orientation will be discussed. Surface electrode dots have been evaporated onto the film to allow electrical measurements. The ferroelectric and fatigue properties of these films have been assessed with respect to non-volatile memory applications. The implications of film quality and thermal processing on the overall ferroelectric performance will be discussed.     

Mobile defect contribution to the dielectric non-linearity of PZT ferroelectric thin films

Abstract

Effect of the speed of bias voltage variation v on the dielectric non-linearity of metal-PZT-metal thin film capacitors has been studied. A distance ΔV between two maxima of C-V dependence on the voltage scale, characteristic for ferroelectric phase, as a function of the v value was investigated. It was established that decreasing vvalue led to ΔV decrease: ΔV = 1.8–2.0 V when v = 1.6x10⁴ V/s, and ΔV ? 1.0 V when v = 6.5x10^?2 V/s. The ΔV(v) dependence can be explained by the decreasing of the coercive field of the film due to the migration of charged mobile defects such as the doubly ionized oxygen vacancies, and the formation of space charge regions near the electrodes. Using the experimental data some parameters of the migration process were evaluated: the concentration of oxygen vacancies and their mobility were found to be about 10²⁴ m^?3 and 10^?11 m²/Vs, respectively. These values are close to the data published in the literature obtained using the alternative methods of investigation.     

Preparation of ferroelectric thin films for Si-based devices

Abstract

Lead titanate (PbTiO₃) thin films have been prepared on titanium dioxide coated silicon wafers by chemical vapor deposition (CVD). The pure PbTiO₃ thin films were deposited by controlling the experimental conditions. The gas phase reaction of TiO₂ occurred by exceeding the critical value of titanium input fraction at constant oxygen partial pressure. Strontium titanate (SrTiO₃) thin films have been prepared on p-type silicon wafers by radio frequency (RF) magnetron sputtering. The SrTiO₃ thin film was polycrystalline and the Sr/Ti ratio of this film was 0.91. The SrTiO₃ thin films contain three regions, an external surface layer, a main layer and an interfacial layer. The stoichiometric SrTiO₃ thin film was obtained by using the SrO excess target. The SrTiO₃ film annealed at 600[ddot]C has an ideal capacitance-voltage (C-V) curve and maximum effective dielectric constant.     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

Low temperature metal-organic chemical vapor deposition of Ru thin films as electrode for high dielectric capacitors

Abstract

Low temperature metal-organic chemical vapor deposition (MOCVD) process of Ru films for use as electrode material was studied using a noble dome type reactor, liquid delivery technique and a new precursor. The films were grown at temperatures ranging from 275°C to 480°C in which film growth was controlled by a surface chemical reaction with a small activation energy of 0.21 eV. The root-mean-squared surface roughness was as low as 23 Å for a film grown at 290°C on a SiO₂ surface.     

Mocvd process model for deposition of complex oxide ferroelectric thin films

Abstract

Thin complex oxide films, such as ferroelectrics, pyroelectrics, waveguides, superconductors, MEMS/MOEMS and piezoelectrics are experiencing rapid growth in a wide variety of commercial markets. In particular, ferroelectrics as used in IC cards, embedded memories with micro-controllers, stand-alone memories, and other ASIC applications, require deposition by a technique that is compatible with deep sub-micron advanced geometry IC integration. Metal Organic Chemical Vapor Deposition (MOCVD) is the deposition method of choice for achieving conformal uniform (composition and thickness) contiguous pin hole free thin films over the challenging sub 0.2 micron geometry topology necessary for implementing advanced devices. MOCVD is free of the physical limitations that produce film defects associated with other liquid source and physical vapor deposition techniques. Of the different MOCVD approaches to complex oxide film deposition, we have found rotating disk reactor (RDR) MOCVD to be the most versatile and capable of producing uniform films efficiently. Using computational fluid dynamic methods, a process model for optimizing the multiple process parameters of RDR-MOCVD, single and multiple wafer production tools, has been developed. The models developed are compatible with plasma-assist, single or multiple precursor and graded composition deposition of films. The developed hardware and model have been combined to maximize thin oxide film properties. SMI modeled RDR MOCVD methodology and film results are presented.     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.