This paper describes a solid-state sensor for ultra-high-speed (UHS) imaging. The ‘Kirana’ sensor was designed and manufactured in a 180 nm CMOS technology to achieve full-frame 0.7 Megapixel video capture at speeds at 2 MHz. The 30 μm pixels contain a pinned photodiode, a set of 180 low-leakage storage cells, a floating-diffusion, and a source follower output structure. Both the individual cells and the way they are arranged in the pixel are novel. The pixel architecture allows correlated double sampling for low noise operation.<p> </p>In the fast mode, the storage cells are operated as a circular buffer, where 180 consecutive frames are stored until receipt of a trigger; up to 5 video-bursts per second can be read out. In the ‘slow’ mode, the storage cells act like a pipeline; the sensor can be read out like a conventional sensor at a continuous frame rate of 1,180 fps. The sensor architecture is fully scalable in resolution since memory cells are located inside each pixel. The pixel architecture is scalable in memory depth (number of frames) as a trade-off with pixel size, dependent on application. The present implementation of 0.7 Mpixels has an array focal plane which is optimized for standard 35 mm optics, whilst offering a competitive 180-frame recording depth.<p> </p>The sensor described has been manufactured and is currently being characterized. Operation of the sensor in the fast mode at 2 million frames per second has been achieved. Details on the camera/sensor operation are presented together with first experimental results.
Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) are commonly used in the analysis of
particulates in fluid flows. Despite the successes of these techniques, current instrumentation has placed limitations on
the size and shape of the particles undergoing measurement, thus restricting the available data for the many industrial
processes now utilising nano/micro particles. Data for spherical and irregularly shaped particles down to the order of 0.1
µm is now urgently required. Therefore, an ultra-fast LDA-PIV system is being constructed for the acquisition of this
A key component of this instrument is the PIV optical detection system. Both the size and speed of the particles under
investigation place challenging constraints on the system specifications: magnification is required within the system in
order to visualise particles of the size of interest, but this restricts the corresponding field of view in a linearly inverse
manner. Thus, for several images of a single particle in a fast fluid flow to be obtained, the image capture rate and
sensitivity of the system must be sufficiently high.
In order to fulfil the instrumentation criteria, the optical detection system chosen is a high-speed, lensed, digital imaging
system based on state-of-the-art CMOS technology - the 'Vanilla' sensor developed by the UK based MI3 consortium.
This novel Active Pixel Sensor is capable of high frame rates and sparse readout. When coupled with an image
intensifier, it will have single photon detection capabilities. An FPGA based DAQ will allow real-time operation with
minimal data transfer.
A United Kingdom consortium (MI3) is founded to develop advanced CMOS image sensors for scientific applications. “Vanilla,” a 520×520 array of active pixels with 25-µm pitch is fabricated in the 0.35-µm 4M2P (4 metal, 2 poly) CMOS process and uses a 3.3-V supply. It has flushed reset circuitry to attain low reset noise and random pixel access for high-speed region-of-interest (ROI) readout. “OPIC” is a 64×72 test structure array of digital pixels with 30-µm pitch, fabricated in 0.25-µm 5M1P (5 metal 1 poly) CMOS process with a 3.3/2.5-V supply. It can perform thresholding via an in-pixel comparator for sparse readout at a high frame rate. Characterization of both sensors is performed under optical illumination and x-ray exposure. For x-ray characterization, both sensors were coupled to a structured thallium-doped cesium iodide (CsI:Tl) scintillator via a fiber optic plate. Vanilla has been found to exhibit 34±3e− read noise and a spectral response of 225±5 mA/W at 500 nm and can read a 6×6 ROI at 24,395 frames/s. OPIC has 46±3e− read noise and can perform sparse readout at up to 3700 frames/s. Based on these results, Vanilla could be employed for applications where only a small portion of the image contains relevant information, while OPIC is suited to high-speed imaging applications.
I-ImaS (Intelligent Imaging Sensors) is a European project aiming to produce adaptive x-ray imaging systems using Monolithic Active Pixel Sensors (MAPS) to create optimal diagnostic images. Initial systems concentrate on mammography and cephalography.
The on-chip intelligence available to MAPS technology will allow real-time analysis of data during image acquisition, giving the capability to build a truly adaptive imaging system with the potential to create images with maximum diagnostic information within given dose constraints.
In our system, the exposure in each image region is optimized and the beam intensity is a function not only of tissue thickness and attenuation, but also of local physical and statistical parameters found in the image itself. Using a linear array of detectors with on-chip intelligence, the system will perform an on-line analysis of the image during the scan and then will optimize the X-ray intensity in order to obtain the maximum diagnostic information from the region of interest while minimizing exposure of less important, or simply less dense, regions.
This paper summarizes the testing of the sensors and their electronics carried out using synchrotron radiation, x-ray sources and optical measurements.
The sensors are tiled to form a 1.5D linear array. These have been characterised and appropriate correction techniques formulated to take into account misalignments between individual sensors.
Full testing of the mammography and cephalography I-ImaS prototypes is now underway and the system intelligence is constantly being upgraded through iterative testing in order to obtain the optimal algorithms and settings.
A UK consortium (MI3) has been founded to develop advanced CMOS pixel designs for scientific applications.
Vanilla, a 520x520 array of 25&mgr;m pixels benefits from flushed reset circuitry for low noise and random pixel access
for region of interest (ROI) readout. OPIC, a 64x72 test structure array of 30&mgr;m digital pixels has thresholding
capabilities for sparse readout at 3,700fps. Characterization is performed with both optical illumination and
x-ray exposure via a scintillator. Vanilla exhibits 34±3e<sup>-</sup> read noise, interactive quantum efficiency of 54% at
500nm and can read a 6x6 ROI at 24,395fps. OPIC has 46±3e<sup>-</sup> read noise and a wide dynamic range of 65dB
due to high full well capacity. Based on these characterization studies, Vanilla could be utilized in applications
where demands include high spectral response and high speed region of interest readout while OPIC could be
used for high speed, high dynamic range imaging.
We describe our programme to develop science-grade CMOS active pixel sensors for future space science missions, and in particular an extreme ultra-violet spectrograph for solar physics studies on the ESA Solar Orbiter. Our goal is the development of a large format 4k x 4k pixel CMOS sensor with useful sensitivity in the extreme ultra-violet (EUV) for solar physics spectroscopy and imaging. Our route to EUV sensitivity relies primarily in adapting the back-thinning and rear-illumination techniques first developed for CCD sensors; however we are also exploring the alternative approach of using a front-etch to expose the CMOS photodiodes. We have successfully back-thinned several 525 x 525 prototype CMOS sensors and proved that the devices survived the process both structurally and functionally. We have also been successful in removing the oxide from the front side of a small array of pixels, using focused ion beam etching. Preliminary results from these pixels show they are sensitive in the Ultra Violet. We have also designed a working large format 4k x 3k prototype on a 0.25 micron CMOS imager process.
A theological model is presented which analyses the sensitivity of composite detectors to a flux of x-rays emerging form a radiological x-ray generator. The model describes the many factor which influenced the x-ray response, for the case where the detector is composed of several layers of crystallites separated by a polymeric glue as is the case of composite HgI<SUB>2</SUB> detectors fabricated by the screen print method. The model also describes the variation of the sensitivity with grain size and dielectric constant, taking into account the dielectric constant of the binder showing also the experimental result. Finally, the experimental result of the sensitivity vs. the voltage is shown for single crystal and composite HgI<SUB>2</SUB> detectors and these results are compared with polycrystalline PbI<SUB>2</SUB> and a-Se, which are the main material candidates for medical digital radiology.
Solid state solutions for imaging are mainly represented by CCDs and, more recently, by CMOS imagers. Both devices are based on the integration of the total charge generated by the impinging radiation, with no processing of the single photon information. The dynamic range of these devices is intrinsically limited by the finite value of noise. Here we present the design of an architecture which allows efficient, in-pixel, noise reduction to a practically zero level, thus allowing infinite dynamic range imaging. A detailed calculation of the dynamic range is worked out, showing that noise is efficiently suppressed. This architecture is based on the concept of single-photon counting. In each pixel, we integrate both the front-end, low-noise, low-power analog part and the digital part. The former consists of a charge preamplifier, an active filter for optimal noise bandwidth reduction, a buffer and a threshold comparator, and the latter is simply a counter, which can be programmed to act as a normal shift register for the readout of the counters' contents. Two different ASIC's based on this concept have been designed for different applications. The first one has been optimized for silicon edge-on microstrips detectors, used in a digital mammography R and D project. It is a 32-channel circuit, with a 16-bit binary static counter.It has been optimized for a relatively large detector capacitance of 5 pF. Noise has been measured to be equal to 100 + 7*Cd (pF) electron rms with the digital part, showing no degradation of the noise performances with respect to the design values. The power consumption is 3.8mW/channel for a peaking time of about 1 microsecond(s) . The second circuit is a prototype for pixel imaging. The total active area is about (250 micrometers )**2. The main differences of the electronic architecture with respect to the first prototype are: i) different optimization of the analog front-end part for low-capacitance detectors, ii) in- pixel 4-bit comparator-offset compensation, iii) 15-bit pseudo-random counter. The power consumption is 255 (mu) W/channel for a peaking time of 300 ns and an equivalent noise charge of 185 + 97*Cd electrons rms. Simulation and experimental result as well as imaging results will be presented.
The silicon microstrips tracker for CMS at LHC demands fast, radiation-hard electronics. An original solution was proposed for the processing of signals from silicon detectors. This technique allows precise reconstruction of the arrival time of the particles, even with a 'slow' shaping time and a limited power budget. This idea was already implemented in the APV6 circuit, designed in a bulk CMOS technology from Harris.In this paper, we present the version (APVD) designed in the CMOS SOI radiation hard technology DMILL by a French-British collaboration. The APVD is a 128-channel mixed analogue-digital: each channel includes a low-noise charge preamplifier, a CR-RC shaper with a peaking time of 50 ns, an analogue pipeline where the signal is sampled at 40 MHz, an analogue pulse shape processor and a current output multiplexer. The circuit integrates an 12C interface for easy control of the operating parameters. All the control current and voltages as well as a calibration pulse are generated internally by dedicated blocks. The design and first experimental results from the first version of the 128-channel APVD, will be presented in this paper. They show the circuit is fully functional and can be used for the CMS experiment.
Recently polycrystalline mercuric iodide have become available, for room temperature radiation detectors over large areas at low cost. Though the quality of this material is still under improvement, ceramic detectors have been already been successfully tested with dedicated low-noise, low-power mixed signal VLSI electronics which can be used for compact, imaging solutions. The detectors used are of different kinds: microstrips and pixels; of different sizes, up to about 1 square inch; and of different thickness, up to 600 microns. The properties of this first-generation detectors are quite uniform from one detector to another. Also for each single detector the response is quite uniform and no charge loss in the inter-electrode space have been detected. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology equipment, which is an attractive feature where low cost and large area applications are needed.
The direct deposition of polycrystalline semiconductor HgI<SUB>2</SUB> detectors on pre-deposited specially designed pixel electrodes is described, using two methods, the hot wall vapor deposition, HWVD, and thick film screen print (SP) methods. Some characterization results of the HgI<SUB>2</SUB> material used to facilitate the detectors are described. The pre-deposited substrate is made by standard hybrid technology. The electrode pattern is a 16*16 pixel square pattern each with a size of 1.48 mm and with 0.1 mm spacing; the total area covered by the pixels is (25.28 mm)<SUP>2</SUP> equals 639.078 mm<SUP>2</SUP>. In order to fan out the pixels to read-out electronics, holes were made through the ceramic thickness and connecting lines were drawn on the opposite side of the ceramic alumina substrate, where complicated patterns can be produced. The pixel detector is tested with beta particles, and data showing the leakage current vs. bias, are given showing a resistivity of about 2*10<SUP>12</SUP> ohm cm. The current and the average charge signal are reported for three different HgI<SUB>2</SUB> pixel detectors. The signal for one of the detectors is about 1100 electrons at 800 V bias voltage and for the second detector, the resistivity is in the same order of magnitude and the charge collection is somewhat better, reaching 1600 electrons at 700 V. One of the detectors was connected to a second hybrid designed for mounting of 8 castor 1.0 chips. CASTOR 1.0 is a VLSI circuit designed for imaging and the results are being evaluated.
Polycrystalline mercuric iodide nuclear radiation detectors have been prepared using different ceramic fabrication methods, such as hot pressing, hot wall vapor phase deposition and screen printing. Areas varying between 0.01 to 100 cm<SUP>2</SUP> and thicknesses varying between 30 to 600 microns, have been fabricated. Gold or carbon electrodes were deposited having the shape of single continuous, linear strip or square pixel contacts and tested for their response to lower and higher gamma energy and beta particles. The (mu) (tau) value is of the order of 10<SUP>-7</SUP> cm<SUP>2</SUP>/V for both holes and electrons and therefore can act as particle counter without energy resolution. THe low production cost for potential large detector area make these compounds interesting for certain imaging applications.