Barium Magnesium Fluoride Research Articles

BaMgF4: An Ultra‐Transparent Two‐Dimensional Nonlinear Photonic Crystal with Strong χ(3) Response in the UV Spectral Region

Ferroelectric patterning is often used in advanced photonics and optoelectronic devices to increase their operational bandwidth and functionality, providing novel and unique performances. However, the extension of the ferroelectric structures to two‐dimensional geometries is currently limited to very few oxides and phosphates systems, which constrains its current and future applications. Here, careful processing based on e‐beam lithography and poling is employed to fabricate the first example of a two‐dimensional nonlinear photonic crystal in Barium Magnesium Fluoride, BaMgF4, a ferroelectric fluoride crystal with an extraordinary transparency ranging from the deep ultraviolet (≈126 nm) to the mid infrared (≈13 μm). The optical characterization shows the possibility of obtaining simultaneously up to three different Cerenkov‐type second harmonic generation processes distributed in a conical geometry via χ(2)‐quasi‐phase‐matching technique. Additionally, the remarkably high χ(3) nonlinear response of BaMgF4 crystal in the UV spectral region is exploited to demonstrate what is believed to be the highest direct UV‐third harmonic generation conversion efficiency in a solid state system via pure χ(3) nonlinear process. Together, the results highlight the outstanding opportunities offered by nonlinear photonic structures as innovative avenues to manipulate the light generation and control with reliable multifunctional optical character.

Formation mechanism of scattering centers in BaMgF 4 single crystals

Barium magnesium fluoride (BaMgF 4—BMF) is a promising material for ultraviolet (UV) all solid-state lasers, but harmful scattering centers are always present in BMF crystals grown by the Czochralski method. In this work, scattering centers were observed only in the middle and upper parts of the as-grown crystals, whereas no light scattering was found in bottom parts. Furthermore, scattering centers can be removed by annealing at temperatures near the melting point, while they can also be created in the originally scatter-free crystals after being annealed at relatively low temperatures. Based on the results of post-growth heat treatments, the presence of a solid solution region near the melting point of BMF is proposed, and scattering centers were attributed to the precipitation of second-phase particles during crystal growth. Combining this hypothesis and the temperature distribution in the growth chamber, we are able to explain the scattering center formation mechanism and their inhomogeneous distribution in the as-grown crystals. This research will enable the growth of higher optical quality BMF crystals used in ultraviolet all solid-state lasers.

Growth and scintillation properties of BaMgF4

By using the micro-pulling down (μ-PD) method, the barium magnesium fluoride (BaMgF4) single crystalline scintillator was produced. The crystal was cut and mirror polished to the physical dimensions of 1×2×10mm3 for examination of scintillation properties. BaMgF4 demonstrated ∼70% transmittance in wavelength range above 170nm, and strong emission peaking around 205nm was observed under X-ray excitation. The absolute light yield of BaMgF4 was 1300±100ph/MeV, and the decay time profile showed two components as 0.57±0.01 (70%) and 2.2±0.31 (30%)ns at room temperature.

Ferroelectric and anisotropic electrical properties of BaMgF4 single crystal for vacuum UV devices

Ferroelectric and anisotropic electrical behaviors of barium magnesium fluoride (BaMgF4) single crystal grown under CF4 atmosphere by the Czochralski method are comprehensively studied by polarization hysteresis and impedance spectroscopy measurements, respectively. The coercive field (Ec) varies not only with applied frequency but also with ramp rates, while spontaneous polarization Ps∼6.9 C/cm2 remains the same. Dielectric polarization and ionic conductivity measurements at various temperatures and frequencies reveal quasi-one-dimensional ionic conduction phenomena along the c-axis and non-Debye dielectric relaxation along the axes.

Photostimulated luminescence and thermoluminescence in europium-doped barium magnesium fluoride

We present the results of thermoluminescence and photostimulated luminescence measurements of BaMgF4, a ferroelectric material which, when doped with divalent europium, can function as an efficient X-ray storage phosphor. While only a broad and largely structureless peak in the photostimulated luminescence excitation spectrum is observed, several trap centres are identifiable in thermoluminescence spectra. The broad peak in the photostimulated luminescence excitation spectrum is deduced to be an R centre and responsible for the observed storage phosphor effect. Madelung energy calculations of the fluorine site potentials in the BaMgF4 crystal structure were performed and indicate that three of the four distinct fluorine sites, F(2)–F(4), are energetically preferred for site vacancies, consistent with the assignment of the electron trap as an R centre.

Characteristics of ferroelectric gate mos and mosfets

Abstract Electrical characteristics of metal-insulator-semiconductor (MIS) capacitors of a variety of ferroelectric materials like lead zirconate titanate (PZT), lead titanate (PT) and barium magnesium fluoride (BMF) on p-silicon have been studied. PZT was deposited by r.f. magnetron sputtering from a composite target and PT from co-evaporation. The films were annealed in oxygen atmosphere in the temperature range 550–700°C for various times. PZT and PT films which are directly deposited on silicon showed low effective dielectric constant.10 For normal applied bias voltages (±5 V), the C-V curves did not show significant hysteresis. The effective dielectric constant was improved significantly by the incorporation of a buffer layer. BMF film was deposited in ultra high vacuum on a heated substrate and the film was encapsulated by a zirconium oxide layer. The C-V curves for these MIS capacitors shows hysteresis and the direction of hysteresis corresponds to ferroelectric polarization.

Characteristics of barium magnesium fluoride (BMF) based MIS capacitors and mfsfets

Abstract BaMgF4 (BMF) films was deposited on p-Si by vacuum evaporation with substrate temperature in the range of 100–400 C. Films deposited at 100 C were amorphous and became polycrystalline at an annealing temperature of 600 C, whereas films deposited above 300 C were polycrystalline. X-ray diffraction shows the formation of orthorombic phase with a = 4.130 A, b = 5.189 A, and c = 14.510 A. The deposited BMF films have been encapsulated with various materials like ZrO2 and amorphous Si. The capacitance-voltage characteristics of MFS capacitors show hysteresis and the direction of hysteresis corresponds to ferroelectric polarization. The current-voltage characteristics of the MOSFETs show a threshold voltage shift which confirms the non-volatile memory behaviour.

BaMgF4 thin film development and processing for ferroelectric FETS

Abstract A ferroelectric memory field-effect transistor (FEMFET) where a ferroelectric thin film is incorporated directly into the gate structure of the transistor is attractive, because it provides not only nonvolatility, but also nondestructive readout (NDRO). At Westinghouse, we are currently developing a FEMFET using thin film barium magnesium fluoride (BaMgF4), a ferroelectric material that was discovered in 1969, but was not fabricated in thin film form until 1989. The BaMgF4 films are grown by evaporation in an ultrahigh vacuum (UHV) chamber on clean Si(100). The natural tendency of these films to grow with the ferroelectric a-axis in the Si(100) plane has been overcome to obtain more random orientation with larger reversible polarization perpendicular to the film. A capping layer (SiO2) has been found to be essential for process integrability of these BaMgF4 films. Ti-W metallization produced only a slight reduction in the capacitance-voltage (C-V) memory window. Switching speed of these films has...

UHV processing of ferroelectric barium magnesium fluoride films and devices

Barium magnesium fluoride (BaMgF4) has recently emerged as a strong candidate for application as the gate dielectric in ferroelectric random access memory (FERRAM) devices with nondestructive readout (NDRO). In earlier papers we reported the successful growth of oriented BaMgF4 films on Si(100) and other substrates in a ultrahigh vacuum (UHV) system, as well as the results of the structural and electrical characterization of these ferroelectric films. In the present paper, we review some of the earlier results, and also examine the effect of variations in the growth temperature and various post-growth anneals on the stoichiometry, crystallinity, orientation, and electrical characteristics of the BaMgF4 films. Initial attempts at integrating the ferroelectric field-effect transistor (FEMFET) with the standard CMOS VLSIC processing, as well as the effect of adding a thin capping layer of SiO2 on the BaMgF4 will also be described.

Electrical characteristics of aluminum-zirconium oxide-barium magnesium fluoride-p silicon MIS capacitors

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.

TdI18: Process integration of the ferroelectric memory FETs (FEMFETs) for ndro ferram

Abstract Experimental results derived from early lots made with modified EEPROM masks are described. MIS structures formed with ferroelectric (FE) films grown on lightly doped silicon substrates have yielded FE switching properties demonstrated by hysteresis in capacitance vs voltage (CV) characteristics as the first step required to show suitability for use in high performance FEMFETs. In particular, switching attributable to polarization charge reversal inside the FE layer is observed, as opposed to tunnel injection of carriers from the silicon into the gate dielectric. Barium magnesium fluoride (BMF) and bismuth titanate FE films are currently under evaluation. Recent FEMFETs have achieved a 9.5V memory window using 20V programming, with Ion/Ioff > 105 for W/L = 12μm/3μm, after complete fabrication ∼ including Scratch-Protection. Some data loss is apparently associated with the BMF films having their primary P. vector nearly in the plane of the film and only a small component of P, experiencing reversal during memory hysteresis programming, as well as the reversable polarization lacking a definite coercive field.

Integration of ferroelectric thin films into nonvolatile memories

Recent advances in the development of high quality thin films of ferroelectric materials have created renewed interest in ferroelectric random access memory (FERRAM) devices. At the present time, several groups are pursuing the development of FERRAMs, where a thin film ferroelectric capacitor memory element is integrated either adjacent to or directly above the circuit elements in a standard silicon or gallium arsenide integrated circuit. However, these designs provide destructive readout (DRO) only. An alternative monolithic device concept, where the ferroelectric thin film is integrated directly into the semiconductor field effect transistor (FET) element, provides not only nonvolatility, but also nondestructive readout (NDRO). For DRO FERRAM structures, lead–zirconate–titanate is the most widely investigated material at present. At Westinghouse, we are concentrating our efforts on the NDRO ferroelectric memory FET approach, using barium magnesium fluoride (BaMgF4) and bismuth titanate (Bi4Ti3O12) thin films. In this paper, we shall review the current status of the integration of ferroelectric thin films into nonvolatile memory devices, with special emphasis on our own results using BaMgF4 and Bi4Ti3O12.