摘要:

Fabrication of nonvolatile memories utilizing ferroelectric polarization charge of lead zirconate-titanate (PZT) thin film capacitors requires the integration of the PZT capacitor process with the semiconductor device processes. This paper discusses the development of enabling process technology for integration of PZT capacitors with GaAs junction field-effect transistors (JFET) on a GaAs wafer for the fabrication of a GaAs ferroelectric random access memory (FERRAM). Individual processes for PZT capacitors and GaAs JFETs are described briefly first. The PZT capacitor process utilizes sol-gel deposition of PZT thin films, while the GaAs JFET process is based on selective ion implantations of silicon and magnesium directly into the GaAs wafer. The integration of these two chemically different processes has been accomplished through process innovations in the areas of sintering of PZT film, ion implantation in GaAs, interconnect metallization and patterning of this metallization. Successful operation of the nonvolatile memory cell has been demonstrated in a memory test circuit fabricated using this integrated process technology.

ISSN:1058-4587    

DOI:10.1080/10584589208215746

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Ferroelectric thin films in the PZT compositional family were prepared by two different solution deposition methodologies. The approaches were based on the use of carboxylate and alkoxide precursors, and acetic acid. Solution aging and mixing order effects on thin film microstructure and ferroelectric properties were studied. Films prepared from 15 day old solutions had a lower remanent polarization (1.4 μC/cm2) and higher coercive field (256 kV/cm) than films prepared from 1 day old solutions (Pr = 18.7 μC/cm2; Ec = 55.2 kV/cm). Raman, FTIR, and NMR spectroscopies were employed to confirm the role of acetic acid in the process, and to begin to understand why changes in solution chemistry can so dramatically affect the resulting film microstructure and properties. FTIR spectroscopy indicated that in addition to acting as a solvent, acetic acid also serves as a chemical modifier in the two processes. That is, it reacts with the alkoxide precursors on a molecular level, replacing the alkoxy ligands. Ester formation was also observed by both FTIR and NMR spectroscopy. The formation of this by-product implies the simultaneous formation of water, and therefore, in-situ hydrolysis and condensation of the precursors.

ISSN:1058-4587    

DOI:10.1080/10584589208215747

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

There are three stages involved in the successful application of a thin film sol-gel oxide, (1) solution synthesis, (2) application, and (3) post application treatments. Each stage contains many processing steps that can be varied in order to optimize the thin film for various applications. This work entails a statistical investigation of a thin film sol-gel PT process for use in memory applications.Statistical experimental design yields a maximum amount of information for a minimum amount of effort. Candidate controllable variables (factors) and responses are first identified. A screening experiment is then conducted to identify the most important factors based on the identified responses. A full-factorial experiment is then conducted to further evaluate the important factors. Finally, a response surface analysis is performed in order to optimize the important factors. Responses such as switching charge (2Pr), endurance and dielectric measurements are used to analyze the sol-gel lead titanate.

ISSN:1058-4587    

DOI:10.1080/10584589208215748

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The general features of the chemistry in synthesizing lead zirconium titanate thin films by PE-MOCVD are discussed based on a preliminary experimental investigation. A qualitative model was constructed as a guide for optimizing the formation of the perovskite phase in the as-deposited condition. This was based on concepts of crystal chemistry of the perovskite and pyrochlore structures and the observed deposition kinetics. Currently, thin films containing up to 92 vol % perovskite have been formed below 500°C in the as-deposited condition. Sufficient latitude remains in adjusting the operating parameters that the formation of phase pure perovskite is considered possible. A thermodynamic analysis of the solid state suggests that low temperature thermal equilibration will yield minority lead-rich phases. Consequently, nonequilibrium processing techniques such as plasma processing are considered necessary. Ferroelectric hysteresis was observed for films receiving post deposition anneals.

ISSN:1058-4587    

DOI:10.1080/10584589208215749

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We have used organometallic chemical vapour deposition (OMCVD) to deposit ferroelectric PbTiO3 films on both single crystalline (001)SrTiO3 and oxidized Si substrates provided with a platinum electrode, using the precursors titanium-iso-propoxide and tetra-ethyl-lead.Epitaxial PbTiO3 layers were grown on (001)SrTiO3 at temperatures around 700°C. The epitaxial nature of the c-axis oriented PbTiO3 is confirmed by Rutherford backscattering spectrometry including channeling, x-ray diffraction (XRD) and high-resolution electron microscopy. A minimum channeling backscatter yield of ∼ 3 % is obtained under optimal conditions.Polycrystalline PbTiO3 films have been deposited on the platinized Si substrates at temperatures between 400°C and 550°C. XRD shows that the films are of a single-phase perovskite-type structure. For a layer deposited at 400°C followed by an anneal at 700°C we measured an Ec of ∼ 100 kV/cm, an Pr of ∼ 55 μC/cm2, and a switching time < 50 ns. This latter value was limited by the instrumental set-up.

ISSN:1058-4587    

DOI:10.1080/10584589208215750

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Lower electrodes for Pb(Zr, Ti)O3 (PZT) used in ferroelectric random access memories must have good electrical conductivity and must interact as little as possible with the PZT film. We have evaluated a number of bottom electrodes for use with PZT films deposited by ion beam sputter deposition These electrodes include Pt, Pt/Ti, RuO2, ReO3, and CoSi23N4, all on SiO2/Si; and TiN and Pt on MgO. Films were studied by XTEM, Auger depth profiling, X-ray microanalysis, and XRD. Important issues for platinum include: a) microstructure (porous for magnetron sputtered Pt); b) rapid lead diffusion through porous Pt; c) adhesion (improved by raising deposition temperature or by adding a titanium layer); and d) hillock formation (related to compressive stress in platinum). RuO2 has good conductivity and has no apparent interfacial layer with PZT. Each of the remaining substrates has drawbacks: CoSi2 forms a surface oxide; ReO3 has poor phase stability; TiN oxidizes and loses conductivity.

ISSN:1058-4587    

DOI:10.1080/10584589208215751

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The Barium Magnesium Fluoride films have been deposited on p-Si wafers at a temperature in the range of 400-450°C in an ion assisted deposition system. X-ray diffraction analysis shows that the films are polycrystalline in nature. The BMF films were encapsulated with an electron beam evaporated Zro2 film of thickness 300°A. The capacitance-voltage (C-V) charactersitics of Aluminum-ZrO2-BMF-p Si MIS capacitors show hysteresis and the direction of the hysterisis correponds to ferroelectric polarization in the BMF film. The shift in threshold voltage was found to depend on bias voltage, ramp rate as well as measurement temperature.

ISSN:1058-4587    

DOI:10.1080/10584589208215752

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The incorporation of a thin film of lithium niobate (LiNbO3) in a conventional MOS (metal-oxide-semiconductor) structure gives the possibility of two fundamentally different types of computer memory architectures. One, based on ferroelectric switching involves the reorganization of charge in the transistor channel to compensate for the change in polarization. Another, based on the bulk photovoltaic effect, involves a shift in the transistor threshold with exposure to differing intensities of incident light. With the use of a molybdenum liftoff process, transistors have been fabricated in which LiNbO3 replaces the usual gate oxide of an MOS transistor. Transistor parameters such as the transconductance, output conductance, and amplification for these devices are reported.

ISSN:1058-4587    

DOI:10.1080/10584589208215753

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The ferroelectric switching properties of thin films of lithium niobate (LiNbO3) on silicon have been investigated. The polarization is shown to be partially reversible with an applied electric field at room temperature. The samples were films of LiNbO3 which were magnetron sputter deposited on silicon substrates. A double pulse method was used to investigate the ferroelectric switching properties of the films. Evidence for partial stable switching of the LiNbO3 film was observed at a field of roughly 500 kV/cm.

ISSN:1058-4587    

DOI:10.1080/10584589208215754

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

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.

ISSN:1058-4587    

DOI:10.1080/10584589208215756

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor