Robert H. Reuss

Effect of growth conditions on surface morphology and photoelectric work function characteristics of iridium oxide thin films

The effect of thermal growth conditions on the morphology and surface work function of iridium oxide thin films grown by annealing Ir thin films in an O2 ambient is presented. The samples were analyzed using x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and photoelectric work function measurements. It is found that, with increasing temperature, IrO2 changes from (110) oriented to a mixture of (110) and (200) during the oxide growth. This is manifested as a sharpening of the photoelectric energy distributions at 800 °C. The surface work function was determined to be 4.23 eV using ultraviolet photoelectron spectroscopy. X-ray photoelectron spectroscopy analysis shows that IrO2 starts to form at 600 °C accompanied by surface roughening. Annealing the Ir film at 900 °C in O2 ambient leads to almost complete desorption of the film.

Field emission characteristics of iridium oxide tips

An important issue in field emission vacuum microelectronics is the stability of the field emitters with the residual ambient gas. Particularly important is that the field emitter tips made of refractory metals like molybdenum, niobium and tungsten are susceptible to oxidation. The corresponding metal oxides are insulating and adversely affect the emission current characteristic by increasing the width of the effective tunneling barrier. With this perspective, we studied iridium oxide field emitters to evaluate the characteristics of conductive oxide tips. We studied the field emission characteristics of iridium and thermally prepared iridium oxide field emitters using field emission microscopy and current–voltage measurements. We found that, upon oxidation, the voltage required to achieve the desired emission current desire dropped significantly. In addition, oxidation led to a decrease of emission current fluctuations. The development of stable conductive oxide field emitters should improve the performa...

Argon inclusion in sputtered films and the effect of the gas on molybdenum field emitter arrays

Residual gas analysis of a number of field emission displays showed that argon desorbed from molybdenum metal lines was the dominant gas in sealed vacuum packages. We present experimental results on the emission characteristics of molybdenum field emitter arrays in argon ambient. In argon, the emission current dropped rapidly similar to that in oxygenic gas ambients. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest a model based on shallow implantation of argon into the field emitter tips that increases the effective width of the tunneling barrier. Experimental support for this model comes from the following observations: emission current degraded only when the device was turned on; after gas exposure, significant current recovery which followed diffusion type behavior was noted; degradation and recovery rates were functions of partial pressure; and no detectable effects associated with sputtering were observed. This mechanism is also consistent with...

Vertical npn transistors by maskless boron implantation

The use of a focused ion beam (FIB) system with a 0.2 μm beam diameter to fabricate npn bipolar transistors by maskless implantation of B (75 keV, 30 mA/cm2) is described. Devices with a conventional boron implant are fabricated on the same wafer. The material (SIMS profile, Rs) and electrical properties (transistor I–V characteristics) of the FIB implants are comparable to those for conventional implants. Initial evaluation suggests that the lateral spread of the implanted area is <0.1 μm. The similarity in results between the two implant processes demonstrates that the FIB system is functioning as designed (no serious problems with beam pointing stability, target current fluctuations, or introduction of impurities, etc.) and that no significant differences in beam target interactions (dopant distribution, percent activation, residual defects, etc.) occur. Application of an FIB lateral base implant to prevent emitter current crowding is discussed and the fabrication of transistors with lateral profiles d...

Fabrication of molybdenum carbide and hafnium carbide field emitter arrays

We report on a process for the fabrication of Mo2C and HfC refractory metal carbide field emitter arrays using a modified Spindt tip fabrication process. Measurements of the aspect ratios of emitter cones showed that Mo2C tip structures have an aspect ratio similar to Mo field emitter tips. Where as with HfC, tip structures with a higher aspect ratio than either Mo or Mo2C were obtained. The measured aspect ratios for Mo, Mo2C, and HfC tips were 1.09, 1.10, and 1.20, respectively. While the target materials to fabricate the arrays were the appropriate carbides, x-ray photoelectron spectroscopy of the carbide films showed evidence for the presence of significant amount of oxygen throughout the films, mostly in the form of oxycarbides. The primary purpose of this report is to describe materials and processes suitable for large area field emission display applications. However, we also provide preliminary electrical results which demonstrate the feasibility of fabrication of metal carbide field emitters and ...

Fabrication of iridium field emitter arrays

Iridium field emitter arrays were fabricated using Spindt tip process. Ir field emitter cones show an aspect ratio of 0.95, slightly less than Mo field emitter arrays fabricated using the same microfabrication process. When compared to the Mo field emitter arrays, the current–voltage characteristics of the Ir arrays were found to scale with the work function difference between Ir and Mo. Under ultrahigh vacuum conditions, the emission current stability of the Ir arrays measured over 180 h was found to be similar or slightly better than the emission stability of Mo arrays. However, when operated in the presence of O2, Ir field emitter arrays proved to be more robust and showed improved emission current stability versus their Mo counterparts.

Real-time measurement of pressure inside field-emission displays

We present a method for nondestructive, real-time measurement of pressure inside sealed flat-panel field-emission displays. Analogous to an ion gauge, field-emitted electrons were used to ionize residual gases within the interelectrode region and the resulting ion current was measured. The procedure was calibrated in a vacuum chamber with known gas pressure. Next, we demonstrated the pressure measurement method inside sealed field-emission displays outfitted with spinning rotor gauge attachments for comparison. We found good correlation between the spinning rotor gauge measurement and the pressure measured by our method. In addition, we observed that the operation of the field-emission display resulted in a rapid drop in pressure similar to ion pumping effects observed in other vacuum electron tubes.

Studies on the interaction between thin film materials and Mo field emitter arrays

A simple method for the evaluation of materials suitable for the fabrication of field emission vacuum microelectronic devices is presented. Since there can be a wide range of electron and ion interactions with the device, it is important to be able to quickly assess if a material may have a particular adverse effect on emission performance under operational conditions. The technique is based on the sensitivity of a large field emitter array to the outgassing or desorption of gas species from thin films under electron beam excitation. We found that Mo field emitter arrays degraded rapidly with stainless steel anodes coated with various oxide materials. The extent of degradation was found to be the most rapid with SiO2, Si3N4, and MoO3 thin films. Stainless steel anodes with Mo and Nb thin films show a faster degradation rate than stainless steel anodes, most likely because of native oxides grown during processing and handling. The emission behavior in the presence of Ir, Pd, Al, Zn, and Ti metal films and ...

Stability and chemical composition of thermally grown iridium-oxide thin films

The effect of growth conditions on the thermal stability and chemical composition of iridium-oxide thin films fabricated by annealing Ir films in O2 is presented. The oxide growth as a function of anneal temperature was studied by x-ray photoelectron spectroscopy depth profile analysis and the thermal stability was determined using temperature programmed desorption spectroscopy. We observed that with increasing anneal temperature, the surface oxidized to IrO2 (110) and the thermal stability of the resulting oxide increased. X-ray photoelectron spectroscopy depth profiles showed that IrO2 starts to form at 600 °C simultaneous with an increase in the surface roughness of the film.

Gas-induced current decay of molybdenum field emitter arrays

Field emission displays can be seriously limited by current degradation of Mofield emitter arrays, primarily due to inadequate vacuum conditions inside their thin vacuum packages. Most lifetime studies describe the deleterious effects of short exposures to oxygenic gases on device performance. Here, we review experimental results on the emission characteristics of molybdenumfield emitter arrays in a variety of gas ambients for extended periods. We find that even in inert gas, the emission current degrades rapidly, comparable to that observed in oxygenic gas ambients. Surprisingly, after exposure when the device is again operated under high vacuum conditions, various levels of current recovery can be observed. No evidence for ion sputter damage is observed. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest that these results point toward a model common for all gaseous ambients based on shallow implantation of ions into the field emitter tips. This creates a near surface layer that modifies the tunneling barrier, and thus subsequently the emission current. Support for this mechanism comes from several experimental observations. The implant degradation model is also consistent with devices that incorporate a field emitterion pump process as a means to reduce pressure in the sealed vacuum package.