Geiger-mode avalanche photodiode detectors are produced using standard CMOS fabrication methods. We
have produced integrated circuits that include the Geiger-mode photodetector and digital signal processing circuits. Our
current design includes sixteen photon counting detector elements, with bias control, active quenching circuits, and
integrated counters at each pixel. The detectors are used to measure chemiluminescence from horseradish peroxidase
conjugated antibodies in sub-microliter samples using an optical waveguide. The detector array has been coupled with an
external field programmable gate array (FPGA) to perform multi-channel, all digital, time resolved fluorescence
measurements of quantum dot nanoparticles and the pH dependence of the fluorescence lifetime of fluorescein dye.
Individual microspheres labeled with a unique barcode and a surface-bound probe are able to provide multiplexed
biological assays in a convenient and high-throughput format. Typically, barcodes are created by impregnating
microspheres with several colors of fluorophores mixed at different intensity levels. The number of barcodes is limited
to hundreds primarily due to variability in fluorophore loading and difficulties in compensating for signal crosstalk. We
constructed a molecular barcode based on differences in lifetimes rather than intensities. Lifetime-based measurements
have an advantage in that signal from neighboring channels is reduced (because signal intensities are equal) and may be
mathematically deconvoluted. The excited state lifetime of quantum dots (QDs) was systematically altered by attaching
a variable number of quencher molecules to the surface. We have synthesized a series of ten QDs with distinguishable
lifetimes all emitting at the same wavelength. The QDs were loaded into microspheres to determine the expected signal
intensities. The uncertainty in lifetimes as a function of the interrogation time was determined. An acceptable standard
deviation (3%) was obtained with a measurement time of approximately 10-30 μsec. Currently, we are expanding these
studies to include multiple wavelengths and determining the maximal number of barcodes for a given spectral window.
Geiger-mode photodiodes (GPD) act as binary photon detectors that convert analog light intensity into digital pulses.
Fabrication of arrays of GPD in a CMOS environment simplifies the integration of signal-processing electronics to
enhance the performance and provide a low-cost detector-on-a-chip platform. Such an instrument facilitates imaging
applications with extremely low light and confined volumes. High sensitivity reading of small samples enables twodimensional
imaging of DNA arrays and for tracking single molecules, and observing their dynamic behavior. In this
work, we describe the performance of a prototype imaging detector of GPD pixels, with integrated active quenching for
use in imaging of 2D objects using fluorescent labels. We demonstrate the integration of on-chip memory and a parallel
readout interface for an array of CMOS GPD pixels as progress toward an all-digital detector on a chip. We also
describe advances in pixel-level signal processing and solid-state photomultiplier developments.
Multi parameter flow cytometry enables detailed identification of cell type and function based on fluorescence
of antibody conjugated dye labels. Current instruments use photomultiplier tube detectors to measure up to eight
fluorescent labels from a single excitation source. We demonstrate polychromatic flow cytometry using a 14-element
avalanche photodiode (APD) array coupled with a dispersive optical grating. Forward scatter, side scatter, and 14
fluorescence channels over the 530 to 800 nm spectral range are recorded using a 16 channel electronics console for
simultaneous event capture. The APD detector elements have a working spectral range from 400 nm to 1050 nm.
Results are presented for flow cytometry measurements of Spherotech UltraRainbow test beads, quantum dot labeled
polystyrene spheres, and cells with antibody conjugated dye labels. The flow cytometry test bead measurements
illustrate the sensitivity and spectral resolution of the APD detector array. The application of the instrument is
demonstrated by identifying CD4 positive lymphocyte populations in normal human whole blood samples.
Commercial flow cytometers use photomultiplier tubes (PMTs) for fluorescence detection. These detectors
have high linear gain and broad dynamic range, but have limited sensitivity in the red and near infrared spectral regions.
We present a comparison of avalanche photodiodes (APDs) and PMTs as detectors in flow cytometry instruments, and
demonstrate improved sensitivity and resolution in the red and near infrared spectral regions using the APD. The
relative performance of the PMT and APD were evaluated by simultaneously measuring the mean fluorescence intensity
and coefficient of variation for emission from light emitting diode pulses, flow cytometry test beads, and fluorescently
labeled cells. The relative signal to noise performance of the APD and PMT was evaluated over the 500 nm to 1050 nm
wavelength range using pulsed light emitting diode light sources. While APDs have higher quantum efficiency but
lower internal gain than PMTs, with appropriate external amplification the APD has signal to noise response that is
comparable to PMTs in the 500 nm to 650 nm range and improved response in the 650 nm to 850 nm range
The data demonstrates that the APD had performance comparable to the PMT in the spectral region between
500 to 650 nm and improved performance in the range of 650 to 1000 nm, where the PMT performance is quite poor.
CD4 positive lymphocyte populations were easily identified in normal human blood both by APD and PMT using
phycoerythrin labeled antibodies. In contrast, only the APD detector could resolve CD4 positive populations using 800
nm Quantum dot labeled antibodies.
We report the development of a photon-counting solid-state photomultiplier that consists of an array of Geiger mode CMOS avalanche photodiodes (APDs). The detector is based on the design described by Buzhan et. al.1 in which the individual outputs of an array of Geiger APDs are coupled together to drive a common output signal. The total output signal is a sum of the Geiger outputs of each individual pixel in the array. For a large array, the sum of the signals from the discrete pixels producess an analog representation of the flux on the detector. In this report we describe our most recent measurements of the spectral response and noise characteristics of the individual detector elements. We present results for a 14 element array of Geiger mode pixels that is used as a solid state photomultiplier (SSPM). We use this SSPM to create a prototype radiation detector that can identify the source based on the energy of the emitted radiation.
We report on the development and application of a flow cytometer using a 16-channel avalanche photodiode (APD) linear detector array. The array is configured with a dispersive grating to simultaneously record emission over a broad wavelength range using the 16 APD channels of the linear APD array. The APD detector elements have a peak quantum efficiency of 80% near 900 nm and have at least 40% quantum efficiency over the 400-nm to 1000-nm wavelength range. The extended red sensitivity of the detector array facilitates the use of lower energy excitation sources and near IR emitting dyes which reduces the impact of autofluorescence in signal starved measurements. The wide wavelength sensitivity of the APD array permits the use of multiple excitation sources and many different fluorescent labels to maximize the number of independent parameters in a given experiment. We show the sensitivity and linearity measurements for a single APD detector. Initial results for the flow cytometer with the 16-element APD array and the 16-channel readout ASIC (application specific integrated circuit) are presented.
Geiger mode Avalanche Photodiodes fabricated using complementary metal-oxide-semiconductor (CMOS) fabrication technology combine high sensitivity detectors with pixel-level auxiliary circuitry. Radiation Monitoring Devices has successfully implemented CMOS manufacturing techniques to develop prototype detectors with active diameters ranging from 5 to 60 microns and measured detection efficiencies of up to 60%. CMOS active quenching circuits are included in the pixel layout. The actively quenched pixels have a quenching time less than 30 ns and a maximum count rate greater than 10 MHz. The actively quenched Geiger mode avalanche photodiode (GPD) has linear response at room temperature over six orders of magnitude. When operating in Geiger mode, these GPDs act as single photon-counting detectors that produce a digital output pulse for each photon with no associated read noise. Thermoelectrically cooled detectors have less than 1 Hz dark counts. The detection efficiency, dark count rate, and after-pulsing of two different pixel designs are measured and demonstrate the differences in the device operation. Additional applications for these devices include nuclear imaging and replacement of photomultiplier tubes in dosimeters.
Avalanche photodiode (APD) arrays fabricated by using complementary metal-oxide-semiconductor (CMOS) fabrication technology offer the possibility of combining these high sensitivity detectors with cost effective, on-board, complementary circuitry. Using CMOS techniques, Radiation Monitoring Devices has developed prototype pixels with active diameters ranging from 5 to 60 microns and with measured quantum efficiencies of up to 65%. The prototype CMOS APD pixel designs support both proportional and Geiger modes of photo-detection. When operating in Geiger mode, these APD’s act as single-optical-photon-counting detectors that can be used for time-resolved measurements under signal-starved conditions. We have also designed and fabricated CMOS chips that contain not only the APD pixels, but also associated circuitry for both actively and passively quenching the self-propagating Geiger avalanche. This report presents the noise and timing performance for the prototype CMOS APD pixels in both the proportional and Geiger modes of operation. It compares the quantum efficiency and dark-count rate of different pixel designs as a function of the applied bias and presents a discussion of the maximum count rates that is obtained with each of the two types of quenching circuits for operating the pixel in Geiger mode. Preliminary data on the application of the APD pixels to laser ranging and fluorescent lifetime measurement is also presented.
An experimental study of the line edge roughness (LER) of nine 193 nm photoresist formulations is presented. In these formulations, the same polymer platform is used while the photoacid generator (PAG) properties and base concentration are systematically varied to produce controlled LER in 130 nm dense line/space features. SEM images of each resist are recorded using a KLA 8250 XR inspection tool. The SEM images are post processed using software developed at Shipley to extract frequency dependent LER as well as RMS amplitude LER. We present an investigation of the dependence of frequency limits and sensitivity on the magnification level and image quality. The primary source of noise in the LER measurements is found to be image amplitude noise, which makes determination of the line edge more difficult. The noise introduced by the line edge measurement errors is primarily high frequency noise.
The top down resist profiles of the different formulations are used to calculate the LER power spectral density functions. While the absolute amplitude of the spectral density functions is different for each resist, all of the plots show a similar functional form. The resists show a maximum amplitude LER near the low frequency limit with an exponential decay at higher frequencies. The log plot of all of the resists show that the LER follows 1/f noise statistics. The dependence of the amplitude of the LER on the aerial image is also demonstrated.
Recently several authors have specifically noted the advantages of using negative tone resists for patterning narrow trenches. The growing interest stems from several factors. Firstly aerial image models indicate that negative tone systems should have improved process windows for patterning narrow trenches, relative to their positive tone counterparts. Secondly, negative tone resists are thought to be advantageous for minimizing variations of CD through pitch for trench layers thus reducing the optical proximity effect for certain exposure conditions. Finally, negative tone systems arguably circumvent the issue of resist poisoning from low k dielectric materials. The combination of these arguments has warranted our effort in the development of negative tone 193 nm resist systems, and this submission will present recent advances in this area. In particular the presentation will focus on prototypical negative tone formulations for use in patterning trenches with bright field imaging. We will present our results on a variety of performance attributes such as dissolution behavior, LER control, etch performance, resolution and process windows for these systems and we will provide a materials basis for using negative tone systems for patterning trenches for back end layers.
This paper describes characterization and lithographic results for one class of low absorbance fluoropolymers that were developed for use in 157 nm lithography. We discuss basic resist properties such as absorbance, hydrophobicity, thickness, resolution and profile for dense 1:1 and semi- dense 1:1.5-10 L/S features, reflection control and plasma etching resistance as a function of composition. Lithographic results were obtained on two types of substrates, silicon and SiON hardmask anti-reflectant. The results on the anti-reflectant were compared to those obtained from simulations using PROLITH. Some of the conclusions of this investigation are: Lower absorbance resists have higher hydrophobicity and better resolution; Resists with high hydrophobicity have very poor adhesion on SiOn, but have very good adhesion on Si and organic anti-reflectants; Only inorganic anti-reflectants have sufficient absorption to provide very low reflectance in <30nm thick films; 100 nm 1:1 L/S resolution is attained in 205 nm thick resist on Si at a resist absorption of 2.2/micrometers . The profile is tapered due to absorption; Adhesion to SiON has been achieved by polymer modification.
This paper discusses the development of a frequency agile receiver for CO2 laser based differential absorption lidar (DIAL) systems. The receiver is based on the insertion of a low-order tunable etalon into the detector field of view. The incorporation of the etalon in the receiver reduces system noise by decreasing the instantaneous spectral bandwidth of the IR detector to a narrow wavelength range centered on the transmitted CO2 laser line, thereby improving the overall D* of the detection system. A consideration of overall lidar system performance result in a projected factor of 2 to 7 reduction in detector system noise, depending on the characteristics of the environment being probed. These improvements can play a key role in extending the ability of DIAL to monitor chemical releases form long standoff distances.
Understanding many-body dynamics on a molecular level is a major aim in condensed phase photodynamical research. Much can be learned about this general field through studies of molecular photodissociation in model systems, namely crystalline rare gas solids. The aim of this presentation is to illustrate this proposition by highlights drawn from a variety of related investigations. Under the title of photodissociation in solids, several related processes can be categorized: charge transfer induced 1 radiative dis sociation ,2 atomic photomobility,3 are examples.