Conventional Charge-coupled Devices Research Articles

Characterization and Optimization of Skipper CCDs for the SOAR Integral Field Spectrograph

We present results from the characterization and optimization of Skipper charge-coupled devices (CCDs) for use in a focal plane prototype for the Southern Astrophysical Research Integral Field Spectrograph (SIFS). We tested eight Skipper CCDs and selected six for SIFS based on performance results. The Skipper CCDs are 6k × 1k, 15 μm pixels, thick, fully depleted, p-channel devices that have been thinned to ∼250 μm, backside processed, and treated with an anti-reflective coating. We demonstrate a single-sample readout noise of <4.3 e− rms pixel−1 in all amplifiers. We optimize the readout sequence timing to achieve a readout noise of 0.5 e− rms pixel−1 after 74 non-destructive measurements, which can be accomplished in a region covering 5% of the detector area in a readout time of <4 minutes. We demonstrate single-photon-counting in all 24 amplifiers (four amplifiers per detector) with a readnoise of σ N ∼ 0.18 e− rms pixel−1 after N samp = 400 samples, and we constrain the degree of nonlinearity to be ≲1% at low signal levels (0 e− to 50 e−). Clock-induced charge (CIC) remains an important issue when the Skipper CCD is configured to provide a large full-well capacity. We achieve a CIC rate of <1.45 × 10−3 e− pixel−1 frame−1 for a full-well capacity of ∼900 e−, which increases to a CIC rate of ∼3 e− pixel−1 frame−1 for full-well capacities ∼40,000–65,000 e−. We also perform conventional CCD characterization measurements such as charge transfer inefficiency (3.44 × 10−7 on average), dark current (∼2 × 10−4 e− pixel−1 s−1), photon transfer curves, cosmetic defects (<0.45% “bad” pixels), and charge diffusion (point-spread function < 7.5 μm) to verify that these properties are consistent with expectations from conventional p-channel CCDs used for astronomy. Furthermore, we provide the first measurements of the brighter-fatter effect and absolute quantum efficiency (≳80% between 450 and 980 nm; ≳90% between 600 and 900 nm) using Skipper CCDs.

Two-dimensional strain mapping in semiconductors by nano-beam electron diffraction employing a delay-line detector

A delay-line detector is established for electron detection in the field of scanning transmission electron microscopy (STEM) and applied to two-dimensional strain mapping in Si-based field effect transistors. We initially outline the functional principle of position-sensitive delay-line detection, based on highly accurate time measurements for electronic pulses travelling in meandering wires. In particular, the detector is a single-counting device essentially providing an infinite time stream of position-resolved events so that acquisition speed is not hindered by detector read-outs occurring in conventional charge-coupled devices. By scanning the STEM probe over stressor- and gate regions of a field effect transistor on a 100 × 100 raster, 10 000 diffraction patterns have been acquired within 3–6.5 min, depending on the scan speed. Evaluation of the 004 and 220 reflections yields lateral and vertical strain at a spatial resolution of 1.6 nm. Dose-dependent strain precisions of 1.2−1.8×10−3 could be achieved for frame times of 40 and 20 ms, respectively. Finally, the detector is characterised as to quantum efficiency and further scopes of application are outlined.

Charge transfer inefficiency in the pre- and post-irradiated Swept Charge Device CCD236

This paper describes the mapping of spectral response of an e2v technologies Swept Charge Device (SCD) CCD236 pre and post irradiation with a 10 MeV equivalent proton fluence of 5.0 × 108 protons cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector which will be used in India's Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) and China's Hard X-ray Modulation Telescope (HXMT). To enable the suppression of surface dark current, clocking is performed continuously resulting in a linear readout. As such the flat field illumination used to measure any change in spectral response over a conventional Charge-Coupled Devices (CCDs) is not possible. An alternative masking technique has been used to expose pinpoint regions of the device to Mn-Kα and Mn-Kβ X-rays, enabling a local map of spectral response to be built up over the device. This novel approach allows for an estimation of the Charge Transfer Inefficiency (CTI) of the device to be made by allowing the creation of a CTI scatter plot similar to that typically observed in conventional CCDs.

Proton irradiation of a swept charge device at cryogenic temperature and the subsequent annealing

A number of studies have demonstrated that a room temperature proton irradiation may not be sufficient to provide an accurate estimation of the impact of the space radiation environment on detector performance. This is a result of the relationship between defect mobility and temperature, causing the performance to vary subject to the temperature history of the device from the point at which it was irradiated. Results measured using Charge Coupled Devices (CCD) irradiated at room temperature therefore tend to differ from those taken when the device was irradiated at a cryogenic temperature, more appropriate considering the operating conditions in space, impacting the prediction of in-flight performance. This paper describes the cryogenic irradiation, and subsequent annealing of an e2v technologies Swept Charge Device (SCD) CCD236 irradiated at −35.4°C with a 10 MeV equivalent proton fluence of 5.0 × 108 protons · cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector that will be flown on-board the Chandrayaan-2 and Hard X-ray Modulation Telescope spacecraft, in the Chandrayaan-2 Large Area Soft X-ray Spectrometer and the Soft X-ray Detector respectively. The SCD is readout continually in order to benefit from intrinsic dither mode clocking, leading to suppression of the surface component of the dark current and allowing the detector to be operated at warmer temperatures than a conventional CCD. The SCD is therefore an excellent choice to test and demonstrate the variation in the impact of irradiation at cryogenic temperatures in comparison to a more typical room temperature irradiation.

Serial time-encoded amplified imaging for real-time observation of fast dynamic phenomena

Ultrafast real-time optical imaging is an indispensable tool for studying dynamical events such as shock waves, chemical dynamics in living cells, neural activity, laser surgery and microfluidics. However, conventional CCDs (charge-coupled devices) and their complementary metal-oxide-semiconductor (CMOS) counterparts are incapable of capturing fast dynamical processes with high sensitivity and resolution. This is due in part to a technological limitation-it takes time to read out the data from sensor arrays. Also, there is the fundamental compromise between sensitivity and frame rate; at high frame rates, fewer photons are collected during each frame-a problem that affects nearly all optical imaging systems. Here we report an imaging method that overcomes these limitations and offers frame rates that are at least 1,000 times faster than those of conventional CCDs. Our technique maps a two-dimensional (2D) image into a serial time-domain data stream and simultaneously amplifies the image in the optical domain. We capture an entire 2D image using a single-pixel photodetector and achieve a net image amplification of 25 dB (a factor of 316). This overcomes the compromise between sensitivity and frame rate without resorting to cooling and high-intensity illumination. As a proof of concept, we perform continuous real-time imaging at a frame speed of 163 ns (a frame rate of 6.1 MHz) and a shutter speed of 440 ps. We also demonstrate real-time imaging of microfluidic flow and phase-explosion effects that occur during laser ablation.

Radiation Tolerance of Fully-Depleted P-Channel CCDs Designed for the SNAP Satellite

Thick, fully depleted p-channel charge-coupled devices (CCDs) have been developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have several advantages over conventional thin, n-channel CCDs, including enhanced quantum efficiency and reduced fringing at near-infrared wavelengths and improved radiation tolerance. Here we report results from the irradiation of CCDs with 12.5 and 55 MeV protons at the LBNL 88-Inch Cyclotron and with 0.1-1 MeV electrons at the LBNL Co60 source. These studies indicate that the LBNL CCDs perform well after irradiation, even in the parameters in which significant degradation is observed in other CCDs: charge transfer efficiency, dark current, and isolated hot pixels. Modeling the radiation exposure over a six-year mission lifetime with no annealing, we expect an increase in dark current of 20 e/pixel/hr, and a degradation of charge transfer efficiency in the parallel direction of 3e-6 and 1e-6 in the serial direction. The dark current is observed to improve with an annealing cycle, while the parallel CTE is relatively unaffected and the serial CTE is somewhat degraded. As expected, the radiation tolerance of the p-channel LBNL CCDs is significantly improved over the conventional n-channel CCDs that are currently employed in space-based telescopes such as the Hubble Space Telescope.

Analysis of noise characteristics for the active pixels in CMOS image sensors for X-ray imaging

CMOS image sensors have poorer performance compared to conventional charge coupled devices (CCDs). Since CMOS Active Pixel Sensors (APSs) in general have higher temporal noise, higher dark current, smaller full well charge capacitance, and lower spectral response, they cannot provide the same wide dynamic range and superior signal to noise ratio as CCDs. In view of electronic noise, the main source for the CMOS APS is the pixel, along with other signal processing blocks such as row and column decoder, analog signal processor (ASP), analog-to-digital converter (ADC), and timing and control logic circuitry. Therefore, it is important and necessary to characterize noise of the active pixels in CMOS APSs, and we performed experimental measurements and comparisons with theoretical estimations. To derive noise source of the pixels, we designed and fabricated four types of CMOS active pixels, and each pixel is composed of a photodiode and three MOS transistors. The size of these pixels is 100 μm×100 μm. The test chip was fabricated using ETRI 0.8 μm (2P/2M) standard CMOS process. It was found that the dominant noise in CMOS active pixels is shot noise during integration under normal operating conditions. And, it was also seen that epitaxial type pixels have similar noise level compared to non-epitaxial type, and the noise of diffusion type pixel is larger than for a well type pixel on the same substrate type.

イメージセンシング技術 天体撮影用の超高感度ハイビジョンカメラ

An ultrahigh-sensitivity color high-definition television (HDTV) camera has been developed. It consists of three proximity-focused image intensifier tubes with a large image size (useful area : 40mm diameter) and three frame-interline-transfer charge-coupled devices (CCDs) (2/3-inch, 2million pixels). The images are relayed by high-quality lenses with a reducing power of 1/3.6. The camera' s sensitivity is 3000times that of conventional HDTV CCD cameras. It can caputre iamges of meteors from the ground and of the various hues of celestial bodies when used with an advanced astronomical telescope.

An Ultrahigh-Sensitivity Color HDTV Camera for Shooting Heavenly Bodies

An ultrahigh-sensitivity color high-definition television (HDTV) camera that consists of three proximity-focused image intensifier tubes of large image size (useful area: 40mm diameter) and three frame interline transfer (FIT) charge-coupled devices (CCDs) of 2/3-in. 2M pixels has been developed. The images are relayed by high-quality lenses with a reducing power of 1/3.6. The camera's sensitivity is 3000 times higher than that of a conventional HDTV CCD camera; it can take rare shots of a meteor from the ground and video images of the various hues of celestial bodies by means of an advanced astronomical telescope.

Thin films applied to integrated optical position-sensitive detectors

We have developed a linear thin film position-sensitive detector with 128 elements, based on p.i.n. a-Si:H devices. The incorporation of this sensor into an optical inspection camera makes possible the acquisition of three-dimensional information of an object, using laser triangulation methods. The main advantages of this system, when compared with the conventional charge-coupled devices, are the low complexity of hardware and software used, and that the information can be continuously processed (analogic detection). In this paper, we present the most significant characteristics of the singular one-dimensional thin film position-sensitive detectors that form part of the linear array with 128 sensors.

A linear array thin film position sensitive detector for 3D measurements

A novel compact linear thin film position sensitive detector with 128 elements, based on p-i-n a-Si:H devices was developed. The proper incorporation of this sensor into an optical inspection camera makes possible the acquisition of three dimension information of an object, using laser triangulation methods. The main advantages of this system, when compared with the conventional charge-coupled devices, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

CCD Quantum Efficiency at the Theoretical Limit with Molecular Beam Epitaxy

A variety of biological, medical, astronomical and materials science measurements require real-time imaging of phenomena which produce low light levels. Charge-coupled devices (CCDs), which have high resolution and linear response over a large dynamic range, are often used as imaging sensors in conjunction with image intensifiers or phosphors to improve the signal-to-noise at low light levels, particularly in the blue and UV regions of the spectrum. Conventional CCDs typically have quantum efficiency (QE) as low as ~10% in the range of 300-500 nm. This region of the spectrum is very important in biological experiments which require detecting the fluorescence of dyes, in astronomical observations of spectral lines in the blue and near UV, and in a variety of applications which use image intensifiers to amplify the signal. Improvement of CCD quantum efficiency with respect to the conventional technology is critical for most of these experiments. The detection of blue and UV photons in a silicon CCD is challenging due to the short absorption length of these photons in silicon (e.g., 4 nm absorption length at 270 nm) and the existence of a backside potential well (caused by positive charge at the interface of Si and SiO2).

Junction charge-coupled logic (JCCL)

Junction charge-coupled devices (JCCDs) offer advantages over conventional charge-coupled devices in the area of logic applications. These advantages are based on the fact that charge can be injected and detected through the steering gates of the JCCD, thus offering the possibility of three-dimensional charge transport. These unique charge injection and detection structures have been used to design basic logic functions, such as AND, OR, INVERT, and REGENERATE. A very simple bipolar process, using only five masking steps and 7.5-/spl mu/m layout rules has been used to show the feasibility of the logic elements. These JCCL devices, intended only for demonstration of the principles, have been operated at clock frequencies up to 5 MHz. Other properties of JCCL devices, such as silicon area used and possibility of applications in multivalued logic circuits make them look very promising. Calculations and experiments have shown that scaling down of the devices will allow clock frequencies of up to 50 MHz.