Alan T. Teruya

Mk x Nk gated CMOS imager

Our paper will describe a recently designed Mk x Nk x 10 um pixel CMOS gated imager intended to be first employed at the LLNL National Ignition Facility (NIF). Fabrication involves stitching MxN 1024x1024x10 um pixel blocks together into a monolithic imager (where M = 1, 2, . .10 and N = 1, 2, . . 10). The imager has been designed for either NMOS or PMOS pixel fabrication using a base 0.18 um/3.3V CMOS process. Details behind the design are discussed with emphasis on a custom global reset feature which erases the imager of unwanted charge in ~1 us during the fusion ignition process followed by an exposure to obtain useful data. Performance data generated by prototype imagers designed similar to the Mk x Nk sensor is presented.

Avalanche transistor selection for long-term stability in streak camera sweep and pulser applications

We have identified the Motorola 2N4014 and 2N5551 and the Raytheon R53944 as three transistor types that exhibit avalanche characteristics and have long term collector breakdown voltage stability superior to other transistors tested. Stability on all types has been improved by power burnin. An automatic avalanche transistor burnin tester has been constructed to allow power burnin of up to 1008 transistors at a time. The tester is controlled by an IBM Personal Computer (PC) and can be programmed to acquire data, unattended, at any desired rate or period. Data are collected from each run and stored on a floppy disk in ASCII format. The data analysis software, RS/1 , was used for analysis and display. Data runs were typically 3 to 4 months long, with readings taken weekly. The transistors were biased into the avalanche or Zener region by individual current sources set to about 20% of the self-avalanche current for each type of transistor. Motorola, Zetex and National transistors were operated at 100 microamperes (pA), and the Raytheon units were operated at 20 pA. The electric field causes migration of material in the high field region at the surface near the collector-base junction, creating the voltage instability.

Development of CCD cameras for soft X-ray imaging at the National Ignition Facility

The Static X-Ray Imager (SXI) is a National Ignition Facility (NIF) diagnostic that uses a CCDcamera to record timeintegrated X-ray images of target features such as the laser entrance hole of hohlraums. SXI has two dedicated positioners on the NIF target chamber for viewing thetarget from above and below, and the X-ray energies of interest are 870 eV for the “soft” channel and 3 – 5 keV for the “hard” channels. The original cameras utilize a large formatbackilluminated 2048 x 2048 CCD sensor with 24 micron pixels. Since the original sensor isno longer available, an effort was recently undertaken to build replacement cameras withsuitable new sensors. Three of the new cameras use a commercially available front-illuminatedCCD of similar size to the original, which has adequate sensitivity for the hard X-ray channelsbut not for the soft. For sensitivity below 1 keV, Lawrence Livermore National Laboratory (LLNL) had additional CCDs back-thinned andconverted to back-illumination for use in the other two new cameras. In this paper we describethe characteristics of the new cameras and present performance data (quantum efficiency, flat field, and dynamic range) for the front- and back-illuminated cameras, with comparisons to the originalcameras.

Performance of a 512 x 512 Gated CMOS Imager with a 250 ps Exposure Time

We describe the performance of a 512x512 gated CMOS read out integrated circuit (ROIC) with a 250 ps exposure time. A low-skew, H-tree trigger distribution system is used to locally generate individual pixel gates in each 8x8 neighborhood of the ROIC. The temporal width of the gate is voltage controlled and user selectable via a precision potentiometer. The gating implementation was first validated in optical tests of a 64x64 pixel prototype ROIC developed as a proof-of-concept during the early phases of the development program. The layout of the H-Tree addresses each quadrant of the ROIC independently and admits operation of the ROIC in two modes. If “common mode” triggering is used, the camera provides a single 512x512 image. If independent triggers are used, the camera can provide up to four 256x256 images with a frame separation set by the trigger intervals. The ROIC design includes small (sub-pixel) optical photodiode structures to allow test and characterization of the ROIC using optical sources prior to bump bonding. Reported test results were obtained using short pulse, second harmonic Ti:Sapphire laser systems operating at λ~ 400 nm at sub-ps pulse widths.

Testing of CMOS Devices in NIF's Harsh Neutron Environment

Vendor supplied CMOS sensors were exposed to 14 MeV neutrons on yield shots in NIF and examined for damage. The sensors were exposed to multiple shots with a maximum fluence on one of the sensors of 4.3E11 n/cm2. The results of post-shot testing will be presented. LLNL is investigating the suitability of CMOS imaging sensors for use in the camera of the ARIANE diagnostic which will mitigate the effects of the NIF neutron environment by dumping photoelectrons during the neutron pulse and then recording an image stored on a long persistence phosphor.

Characterization and Compensation of High Speed Digitizers

Increasingly, ADC technology is being pressed into service for single-shot instrumentation applications that were for merely served by vacuum-tube based oscilloscopes and streak cameras. ADC technology, while convenient, suffers significant performance impairments. Thus, in these demanding applications, a quantitative and accurate representation of these impairments is critical to an understanding of measurement accuracy. We have developed a phase-plane behavioral model, implemented it in SIMULINK and applied it to interleaved, high-speed ADCs (up to 4 gigasamples/sec). We have also developed and demonstrated techniques to effectively compensate for these impairments based upon the model

The Effects Of Variations In The Photocathode Voltages Of Electronic Streak Cameras

Electronic streak cameras are used to record subnanosecond data at the Nevada Test Site. It has been found that externally induced variations in the photocathode voltage of the streak tube can produce both temporal and spatial errors on the output image. An elec on beam tracing code was used to model the magnification as a function of photocathode voltage and signal input position for streak tubes manufactured by RCA, ITT, and Kentech. Las tests were also performed where pulsed and radio frequency signals were induced upon the photocathode and the errors on e resultant image were compared with e error sredict-s by the electron II - am code. Also, methods for processing the distortion in digitized images were investigated. This pas r will discuss the results of these investigations.

Increasing Sensitivity Of A Deflection Measurement System

Synchronous demodulation was applied to the Laser Optical Line of Sight system (LOLOS) used to measure deflections of a canister used in underground testing. The purpose of this was to achieve greater sensitivity and resolution than that found in the original system. Electronics and optical equipment were built or acquired to evaluate the concept. Under laboratory conditions sensitivity to lateral and angular displacements were improved by more than an order of magnitude.