P.T. Joseph

On the mechanism of enhancement on electron field emission properties for ultrananocrystalline diamond films due to ion implantation

The effects of N and C ion implantations on modifying the structural and field emission properties of ultrananocrystalline diamond (UNCD) films were investigated. Low dose ion implantations possibly introduced point defects, which were easily removed by the annealing process. The nature of the doping species, N or C, was immaterial. In contrast, high dose N ion implantation induced the formation of the amorphous phase, which was converted into the graphitic phase after annealing, and improved the field emission properties (Je was increased to ~6.3 mA cm−2 at 20 V µm−1). However, the high dose C ion implantation induced the graphitic phase directly, which degraded the field emission characteristics, i.e. Je was lowered to ~0.6 mA cm−2 at 20 V µm−1. The variations in the electron field emission properties for ion-implanted UNCD films are accounted for by the nature of the induced defects and the electron transfer doping mechanism.

Monolithic n-type conductivity on low temperature grown freestanding ultrananocrystalline diamond films

We report monolithic n-type conductivity on low-temperature (<570 °C) grown ultrananocrystalline diamond (UNCD) films by Li-diffusion (about 255 nm) from LiNbO3 substrates. Low resistivity of 1.2 Ω cm with carrier concentration of −2×1020 cm−3 is obtained on freestanding UNCD films. The films bonded to Cu-tape show very low turn-on field of 4.2 V/μm with emission current density of above 0.3 mA/cm2 at a low applied filed of 10 V/μm. The n-type conductivity of low-temperature Li-diffused UNCD films overwhelms that of the high-temperature (≥800 °C) nitrogen doped ones and will make a significant impact to diamond-based electronics.

Field emission enhancement in ultrananocrystalline diamond films by in situ heating during single or multienergy ion implantation processes

The single or multienergy nitrogen (N) ion implantation (MENII) processes with a dose (4×1014 ions/cm2) just below the critical dose (1×1015 ions/cm2) for the structural transformation of ultrananocrystalline diamond (UNCD) films were observed to significantly improve the electron field emission (EFE) properties. The single energy N ion implantation at 300 °C has shown better field emission properties with turn-on field (E0) of 7.1 V/μm, as compared to room temperature implanted sample at similar conditions (E0=8.0 V/μm) or the pristine UNCD film (E0=13.9 V/μm). On the other hand, the MENII with a specific sequence of implantation pronouncedly showed different effect on altering the EFE properties for UNCD films, and the implantation at 300 °C further enhanced the EFE behavior. The best EFE characteristics achieved for the UNCD film treated with the implantation process are E0=4.5 V/μm and current density of (Je)=2.0 mA/cm2 (at 24.5 V/μm). The prime factors for improving the EFE properties are presumed to...

Effect of High-Q Ba4Ti13O30 Materials on The Dielectric Properties of (Bax,Sr1−x)Tio3 Films For Microwave Communication

Nano-sized BaTiO3, SrTiO3 and TiO2 powders have been used to synthesize (Ba x ,Sr1−x )TiO3 materials via mixed oxide process. Then (Ba x ,Sr1−x )TiO3 (BST) (x = 0.5 and 0.6) with addition of high-Q (quality factor) Ba4Ti13O30 (BT) materials were screen printed on Al2O3 substrates. The prepared thick films of BST/BT with three layered and five layered composite materials were sintered at 1275°C (4 h). The microwave dielectric properties of the bulk ceramics and the thick films were measured by resonant cavity method at higher microwave frequencies (9.5 GHz). The three layered thick films have dielectric constant of 13.4 for x = 0.5 and 15.5 for x = 0.6. The five layered thick films possess dielectric constant of 12.7 for x = 0. 5 and 15.8 for x = 0.6. The frequency × quality factor (f × Q) increases markedly with a larger magnitude of 1600 for the three layered thick films than the five layered ones. The results imply that the BST/BT composite thick films have potential application in tunable microwave devices.

MICROWAVE PROPERTIES OF BST AND BST/BMT THIN FILMS GROWN ON SAPPHIRE SUBSTRATE BY EVANESCENT MICROWAVE PROBE

ABSTRACT Thin films of BaxSr1−xTiO3 (BST) serial materials have the advantages of adjustable tunability and are good candidates for the application in DRAM and microwave devices. However, these films usually have loss tangent higher than the order of 0.01 at microwave frequencies. To improve the crystal structures and suppress the microwave losses, an interlayer material with good microwave properties can be used. In this present work, a low loss Ba(Mg1/3Ta2/3)O3 (BMT) thin buffer layer with varying thickness and its effect on the microwave properties of Ba0.4Sr0.6TiO3 thin films is investigated. Moreover, to overcome the spatial limit in the traditional microwave measurement, a novel technique, evanescent microwave probe (EMP) method, is used to directly probe the microwave dielectric properties of the films. This technique also provides the capability to study the dielectric mechanism in micro-scale region. Pulsed laser deposition technique was used to synthesize thin films. The films shows (111) preferably oriented growth of BST films with the introduction of BMT layer for the films grown on sapphire substrates. As the thickness of BMT increases, this behavior is more obvious. The microwave dielectric constants (ϵ) and dielectric losses (tan δ) of the films grown on sapphire substrates have been measured by EMP. The dielectric constants of BST thin films decrease monotonously with the increase of BMT thickness. In contrast, the tan δ shows a discontinuity variation when the BMT buffer layer is deposited for 10–20 minutes.