Process technology and characterization for field emission devices

Vacuum microelectronics is a new research field which applies semiconductor process technology to the fabrication of micron-dimensioned electron devices. Vacuum microelectronics is made possible by advances in microstructures and nanofabrication technology. Vacuum microelectronic devices are further characterized by a wide operating temperature range, nuclear radiation immunity, higher emission current density potential, and lower power consumption than that of thermionic emitters. The low mass of the electron provides a higher carrier mobility than GaAs or any solid state device. These features offer the potentials for wide variety of applications. In this dissertation. electron field emission structures applicable to a variety of vacuum microelectronic devices have been fabricated and characterized. The cathodes are micromachined of N-type silicon and tungsten using a combination of ultraviolet liftoff lithography and reactive ion etching. A minor emphasis has been placed on micromachining surface-grooved structures for applications that include both vacuum microelectronics and optical microsystems. Optimized processing, device modeling, and physical/electrical characterization are key elements in the research described. The control of sidewall angle, cavity depth, and apex radius for ridge structures in silicon has been a major focus of this thesis. Reactive ion etching techniques have been studied for sidewall angles up to 45° and ridge apex radii of approximately 40nm. A fluorine-based chemistry (CF4/O2) with oblique angles ( tilted wafers) for the incident beam electric field and overetching is used in separate experiments. The use of deep UV-hardened photoresist and image-reversal aluminum liftoff for reactive ion etching masking are compared. Aluminum as a shadow mask for reactive ion etching micromachining has the advantage of lower etch/sputtering rates and higher temperature tolerance compared to photoresist in the CF4/O2 system. Typical etch conditions used were CF4/O2 flow rates of 20/2 sccm, pressure 10 to 40 mTorr. and etch duration 30 min. This thesis is one of the first detailed studies of reactive ion etching comparing tilted and untilted wafer substrates. A new process technology for vacuum microelectronic diodes is shown, and device design with a knife-edge cathode and a lateral electron trajectory is implemented as a characterization tool. The cathode structure for these devices consists of a titanium:tungsten /tungsten film sandwich overlaying an aluminum adhesion and sacrificial film. The aluminum film is partially sacrificed to achieve the necessary sharp edge of tungsten metal surface for field emission. The tungsten and titanium metals are deposited by dc magnetron sputtering followed by liftoff lithography and thermal annealing. Selected devices with a cathode to anode spacing of 0.8 μm are electrically characterized in 2 to 5 x10-9 Torr vacuum. A maximum static current of 26μA current is obtained. The I-V characteristics of lateral trajectory devices with a knife-edge cathode are compared with Fowler Nordheim theory. Good agreement occurs if the cathode apex radius is approximately l0nm. Based on a Fowler Nordheim model the effective fraction γ of the knife-edge emitting electrons is in the range 3 to 80%. This research includes the first experimental verification of the effect of deflection electrodes to confine the electron beam. Characterization and modeling comparisons for vacuum microelectronic devices with a knife-edge cathode and lateral electron trajectory are described for the first time

Effects of the Spin-Orbit Coupling and the Superconductivity in simple-cubic alpha-Polonium

We have investigated the mechanism of stabilizing the simple-cubic (SC) structure in polonium (alpha- Po), based on the phonon dispersion calculations using the first-principles all-electron band method. We have demonstrated that the stable SC structure results from the suppression of the Peierls instability due to the strong spin-orbit coupling (SOC) in alpha-Po. Further, we have explored the possible superconductivity in alpha-Po, and predicted that it becomes a superconductor with Tc ~ 4 K. The transverse soft phonon mode at q ~ 2/3 R, which is greatly influenced by the SOC, plays an important role both in the structural stability and the superconductivity in alpha-Po. We have discussed effects of the SOC and the volume variation on the phonon dispersions and superconducting properties of alpha-Po.Comment: 5pages, 5figure

Pressure-induced Phonon Softenings and the Structural and Magnetic Transitions in CrO2_{2}

To investigate the pressure-induced structural transitions of chromium dioxide (CrO$_{2}$), phonon dispersions and total energy band structures are calculated as a function of pressure. The first structural transition has been confirmed at P$\approx$ 10 GPa from the ground state tetragonal CrO$_{2}$ (t-CrO$_{2}$) of rutile type to orthorhombic CrO$_{2}$ (o-CrO$_{2}$) of CaCl$_{2}$ type. The half-metallic property is found to be preserved in o-CrO$_{2}$. The softening of Raman-active B$_{1g}$ phonon mode, which is responsible for this structural transition, is demonstrated. The second structural transition is found to occur for P$\geq$ 61.1 GPa from ferromagnetic (FM) o-CrO$_{2}$ to nonmagnetic (NM) monoclinic CrO$_{2}$ (m-CrO$_{2}$) of MoO$_{2}$ type, which is related to the softening mode at {\bf q} = R(1/2,0,1/2). The third structural transition has been newly identified at P= 88.8 GPa from m-CrO$_{2}$ to cubic CrO$_{2}$ of CaF$_{2}$ type that is a FM insulator

Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO2_{2}

To explore the driving mechanisms of the metal-insulator transition (MIT) and the structural transition in VO2, we have investigated phonon dispersions of rutile VO2 (R-VO2) in the DFT and the DFT+U (U : Coulomb correlation) band calculations. We have found that the phonon softening instabilities occur in both cases, but the softened phonon mode only in the DFT+U describes properly both the MIT and the structural transition from R-VO2 to monoclinic VO2 (M1-VO2). This feature demonstrates that the Coulomb correlation effect plays an essential role of assisting the Peierls transition in R-VO2. We have also found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable under high pressure. We have predicted a new phase of VO2 at high pressure that has a monoclinic CaCl2-type structure with metallic nature

Naphthalimide Trifluoroacetyl Acetonate: A Hydrazine-Selective Chemodosimetric Sensor

The trifluoroacetyl acetonate naphthalimide derivative 1 has been synthesized in good yield. In acetonitrile solution, compound 1 reacts selectively with hydrazine (NH2NH2) to give a five-membered ring. This leads to OFF-ON fluorescence with a maximum intensity at 501 nm as well as easily discernible color changes. Based on a readily discernible and reproducible 3.9% change in overall fluorescence intensity, the limit of detection for 1 is 3.2 ppb (0.1 mu M), which is below the accepted limit for hydrazine set by the U.S. Environmental Protection Agency (EPA). Compound 1 is selective for hydrazine over other amines, including NH4OH, NH2OH, ethylenediamine, methylamine, n-butylamine, piperazine, dimethylamine, triethylamine, pyridine, and is not perturbed by environmentally abundant metal ions. When supported on glass-backed silica gel TLC plates, compound 1 acts as a fluorimetric and colorimetric probe for hydrazine vapor at a partial pressure of 9.0 mm Hg, with selectivity over other potentially interfering volatile analytes, including ammonia, methylamine, n-butylamine, formaldehyde, acetaldehyde, H2O2, HCl, and CO2 being observed. Probe 1 can also be used for the detection of hydrazine in HeLa cells and does so without appreciable interference from other biologically abundant amines and metal ions.U.S. National Science Foundation CHE-1057904Robert A. Welch Foundation F-1018CRI project grant from National Research Foundation of Korea (NRF)Korea government (MSIP) 2009-0081566Chemistr

Second Stage Short Run (X,vc) and (X,sc) Control Charts

In their'70 paper titled "Mean and Variance Control Chart Limits Based on a Small Number of Subgroups" (Journal of Quality Technology, Volume 2, Number 1, pp. 9-16), Yang and Hillier originally derived equations for calculating the factors required to determine second stage short run control limits for ) v,X c( and )s ,X( c charts. Two issues have restricted the applicability of this particular control chart methodology. These are the limited tabulated values of factors Yang and Hillier present and no example to illustrate the use of the methodology. This paper addresses the first issue by presenting a computer program that accurately calculates the factors regardless of the values of the required inputs. An example shows how to incorporate the methodology into a two stage short run control charting procedure. The computer program is available at http://program.20m.com.

Multimedia Distribution Process Tracking for Android and iOS

The crime of illegally filming and distributing images or videos worldwide is increasing day by day. With the increasing penetration rate of smartphones, there has been a rise in crimes involving secretly taking pictures of people's bodies and distributing them through messengers. However, little research has been done on these related issue. The crime of distributing media using the world's popular messengers, WhatsApp and Telegram, is continuously increasing. It is also common to see criminals distributing illegal footage through various messengers to avoid being caught in the investigation network. As these crimes increase, there will continue to be a need for professional investigative personnel, and the time required for criminal investigations will continue to increase. In this paper, we propose a multimedia forensic method for tracking footprints by checking the media information that changes when images and videos shot with a smartphone are transmitted through instant messengers. We have selected 11 of the world's most popular instant messengers and two secure messengers. In addition, we selected the most widely used Android and iOS operating systems for smartphones. Through this study, we were able to confirm that it is possible to trace footprints related to the distribution of instant messengers by analyzing transmitted images and videos. Thus, it was possible to determine which messengers were used to distribute the video when it was transmitted through multiple messengers.Comment: 10 page