Dennis D. Rathman

Megapixel CMOS image sensor fabricated in three-dimensional integrated circuit technology

A 1024/spl times/1024 integrated image sensor with 8 /spl mu/m pixels, is developed with 3D fabrication in 150 mm wafer technology. Each pixel contains a 2 /spl mu/m/spl times/2 /spl mu/m/spl times/7.5 /spl mu/m 3D via to connect a deep depletion, 100% fill-factor photodiode layer to a fully depleted SOI CMOS readout circuit layer. Pixel operability exceeds 99.9%, and the detector has a dark current of <3 nA/cm/sup 2/ and pixel responsivity of /spl sim/9 /spl mu/V/e at room temperature.

Arrays of gated field‐emitter cones having 0.32 μm tip‐to‐tip spacing

We have reduced the gate voltage required to achieve a given emission current density in field‐emitter arrays by scaling down the gate‐to‐tip and tip‐to‐tip spacing to the unprecedented levels of 0.08 and 0.32 μm, respectively. The submicrometer features of our arrays are patterned using interferometric lithography. Electrical tests of arrays we have fabricated have shown a record low turn‐on voltage of 8 V for cesiated molybdenum emitters. Emission current densities of 1600 A/cm2 have been obtained, which is also a record for such structures. These arrays provide large advantages for applications such as flat panel displays and microwave devices.

Comparison of laser‐initiated and thermal chemical vapor deposition of tungsten films

ArF excimer laser radiation has been used to deposit W films on silicon and on SiO2 by initiating the gas phase reaction of WF6 with H2. Deposition rates >100 nm/min and film resistivities as low as two times the bulk value have been obtained at deposition temperatures of 440 °C. The properties of the laser‐deposited films are compared with those of fims obtained using conventional thermal deposition techniques. Film resistivity correlates with the microstructure which in turn depends on the deposition temperature; above 350 °C the low‐resistivity α‐W phase dominates.

Electrical properties of laser chemically doped silicon

The electrical properties of single‐crystal and amorphous Si, doped using a pulsed UV laser, have been studied as a function of laser wavelength and fluence and of UV dose. BCl3 or PCl3 parent gases were used to provide B or P dopant atoms. Dissociation of molecules adsorbed on the Si surface can supplement photolysis of gas‐phase molecules as a source of doping atoms.

Observation of electric field gradients near field‐emission cathode arrays

The variation of electric field gradient above arrays of field emission cathodes has been investigated using atomic force microscopy. The spatial distribution of electric field gradient was obtained as a function of bias and height. Results show a parabolic relationship between the sample bias and electric field gradient. Furthermore, the height dependence of the field gradient is found to follow a power law relationship. These new results demonstrate that force‐gradient atomic force microscopy is capable of providing a direct visual presentation of the variation of field gradients above submicron‐periodicity field emitter arrays.

Bright‐field analysis of field‐emission cones using high‐resolution transmission electron microscopy and the effect of structural properties on current stability

High‐resolution transmission electron microscopy has been used to analyze 150 nm diameter by 150 nm high polycrystalline molybdenum field‐emission cones. The analysis shows that the cones comprise 5 to 10 nm thick grains with tips having gross radii of curvature of about 5 nm and protrusions having radii of curvature of about 1 nm. Such small protrusions may explain why analysis of experimental emission data indicates that the effective emission area of such tips is only 0.1 to 0.5 nm.2 Furthermore, the fact that the structure is composed of small grains indicates that there is a substantial number of molybdenum atoms at grain boundaries and that many configurations of grains and boundaries are possible with minimal free energy. A qualitative model is proposed which links the structural properties to current stabilization and hydrogen passivation effects.

CCD soft-X-ray detectors with improved high- and low-energy performance

We describe results from recent efforts to enhance the performance of CCDs to both low- and high-energy soft a rays. For improved low-energy (E<500 eV) sensitivity we show that a low-temperature surface treatment on back-illuminated devices results in generally better performance than that achieved on devices flown on Chandra, which had a more process-intensive high-temperature treatment. For improved high-energy response we describe a design approach for MOS CCDs that allows high substrate biases for deep depletion (>160 /spl mu/m) and thus improved x-ray detection for E>5 keV.

Genosensors: microfabricated devices for automated DNA sequence analysis

A new technology is introduced for developing potentially low cost, high throughput DNA sequence analysis. This approach utilizes novel bioelectronic genosensor devices to rapidly detect hybridization events across a DNA probe array. Detection of DNA probe/target hybridization has been achieved by two electronic methods. The first method utilizes a permittivity chip which interrogates the miniature test fixtures with a low voltage alternating electric field. The second method, which is the emphasis of this paper, utilizes a charge- coupled device (CCD) to detect the hybridization of appropriately tagged (radioisotope, fluorescent, or chemiluminescent labels) target DNA to an array of DNA probes immobilized above the pixels. Such direct electronic-biologic coupling is shown to provide a tenfold sensitivity improvement over conventional lens-based detection systems.

High-speed, electronically shuttered solid-state imager technology (invited)

Electronically shuttered solid-state imagers are being developed for high-speed imaging applications. A 5 cm×5 cm, 512×512-element, multiframe charge-coupled device (CCD) imager has been fabricated for the Los Alamos National Laboratory DARHT facility that collects four sequential image frames at megahertz rates. To operate at fast frame rates with high sensitivity, the imager uses an electronic shutter technology designed for back-illuminated CCDs. The design concept and test results are described for the burst-frame-rate imager. Also discussed is an evolving solid-state imager technology that has interesting characteristics for creating large-format x-ray detectors with short integration times (100 ps to 1 ns). Proposed device architectures use CMOS technology for high speed sampling (tens of picoseconds transistor switching times). Techniques for parallel clock distribution, that triggers the sampling of x-ray photoelectrons, will be described that exploit features of CMOS technology.

High frequency performance of a fully depleted 0.25-/spl mu/m SOI CMOS technology

A fully depleted (FD) 0.25-/spl mu/m silicon-on-insulator (SOI) CMOS process technology has been developed and established at Lincoln Laboratory. Here we describe the FDSOI process technology, report the high frequency performance of 0.25-/spl mu/m n- and p-channel MOSFETs and digital and analog circuits, and predict the performance of the FDSOI technology scaled to 0.1-/spl mu/m gate lengths.