Jamie Crooks

Monolithic Active Pixel Sensors (MAPS) in a quadruple well technology for nearly 100% fill factor and full CMOS pixels

In this paper we present a novel, quadruple well process developed in a modern 0.18 μm CMOS technology called INMAPS. On top of the standard process, we have added a deep P implant that can be used to form a deep P-well and provide screening of N-wells from the P-doped epitaxial layer. This prevents the collection of radiation-induced charge by unrelated N-wells, typically ones where PMOS transistors are integrated. The design of a sensor specifically tailored to a particle physics experiment is presented, where each 50 μm pixel has over 150 PMOS and NMOS transistors. The sensor has been fabricated in the INMAPS process and first experimental evidence of the effectiveness of this process on charge collection is presented, showing a significant improvement in efficiency.

A novel CMOS monolithic active pixel sensor with analog signal processing and 100% fill factor

We have designed and fabricated a CMOS monolithic active pixel sensor (MAPS) in a novel 0.18 micrometer image-sensor technology (INMAPS) which has a 100% fill factor for charged particle detection and full CMOS electronics in the pixel. The first test sensor using this technology was received from manufacture in July 2007. The key component of the INMAPS process is the implementation of a deep p-well beneath the active circuits. A conventional MAPS design for charged-particle imaging will experience charge sharing between the collection diodes and any PMOS active devices in the pixel which can dramatically reduce the efficiency of the pixel. By implementing a deep p-well, the charge deposited in the epitaxial layer is reflected and conserved for collection at only the exposed collection diode nodes. We have implemented two pixel architectures for charged particle detection. The target application for these pixels is for the sensitive layers of an electromagnetic calorimeter (ECAL) in an international linear collider (ILC) detector. Both pixel architectures contain four n- well diodes for charge-collection; analog front-end circuits for signal pulse shaping; comparator for threshold discrimination; digital logic for threshold trim adjustment and pixel masking. Pixels are served by shared row-logic which stores the location and time-stamp of pixel hits in local SRAM, at the bunch crossing rate of the ILC beam. The sparse hit data are read out from the columns of logic after the bunch train. Here we present design details and preliminary results.

Multimass velocity-map imaging with the Pixel Imaging Mass Spectrometry (PImMS) sensor: an ultra-fast event-triggered camera for particle imaging.

We present the first multimass velocity-map imaging data acquired using a new ultrafast camera designed for time-resolved particle imaging. The PImMS (Pixel Imaging Mass Spectrometry) sensor allows particle events to be imaged with time resolution as high as 25 ns over data acquisition times of more than 100 μs. In photofragment imaging studies, this allows velocity-map images to be acquired for multiple fragment masses on each time-of-flight cycle. We describe the sensor architecture and present bench-testing data and multimass velocity-map images for photofragments formed in the UV photolysis of two test molecules: Br(2) and N,N-dimethylformamide.

PImMS, a fast event-triggered monolithic pixel detector with storage of multiple timestamps

PImMS, or Pixel Imaging Mass Spectrometry, is a novel high-speed monolithic CMOS imaging sensor tailored to mass spectrometry requirements, also suitable for other dark-field applications. In its application to time-of-flight mass spectrometry, the sensor permits ion arrival time distributions to be combined with 2D imaging, providing additional information about the initial position or velocity of ions under study. PImMS1, the first generation sensor in this family, comprises an array of 72 by 72 pixels on a 70 μm by 70 μm pitch. Pixels independently record digital timestamps when events occur over an adjustable threshold. Each pixel contains 4 memories to record timestamps at a resolution of 25 ns. The sensor was designed and manufactured in the INMAPS 0.18 μm process. This allows the inclusion of significant amounts of circuitry (over 600 transistors) within each pixel while maintaining good detection efficiency. We present an overview of the pixel and sensor architecture, explain its functioning and present test results, ranging from characterisation of the analogue front end of the pixel, to verification of its digital functions, to some first images captured on mass spectrometers. We conclude with an overview of the upcoming second generation of PImMS sensors.

The application of the fast, multi-hit, pixel imaging mass spectrometry sensor to spatial imaging mass spectrometry

Imaging mass spectrometry is a powerful technique that allows chemical information to be correlated to a spatial coordinate on a sample. By using stigmatic ion microscopy, in conjunction with fast cameras, multiple ion masses can be imaged within a single experimental cycle. This means that fewer laser shots and acquisition cycles are required to obtain a full data set, and samples suffer less degradation as overall collection time is reduced. We present the first spatial imaging mass spectrometry results obtained with a new time-stamping detector, named the pixel imaging mass spectrometry (PImMS) sensor. The sensor is capable of storing multiple time stamps in each pixel for each time-of-flight cycle, which gives it multi-mass imaging capabilities within each pixel. A standard velocity-map ion imaging apparatus was modified to allow for microscope mode spatial imaging of a large sample area (approximately 5 × 5 mm(2)). A variety of samples were imaged using PImMS and a conventional camera to determine the specifications and possible applications of the spectrometer and the PImMS camera.

A Low Noise Pixel Architecture for Scientific CMOS Monolithic Active Pixel Sensors

This paper presents the design and characterisation of FORTIS (4T Test Image Sensor), which is a low noise, CMOS monolithic active pixel sensor for scientific applications. The pixels present in FORTIS are based around the four transistor (4T) pixel architecture, which is already widely used in the commercial imaging community. The sensor design contains thirteen different variants of the 4T pixel architecture to investigate the effects of changing its core parameters. The variants include differences in the pixel pitch, the diode size, the in-pixel source follower, and the capacitance of the floating diffusion node (the input node of the in-pixel source follower). Processing variations have also been studied, which include varying the resistivity of the epitaxial layer and investigating the effects of a special deep p-well layer. By varying these parameters, the 4T pixel architecture can be optimised for scientific applications where detection of small amounts of charge is required.

Design and performance of a CMOS study sensor for a binary readout electromagnetic calorimeter

We present a study of a CMOS test sensor which has been designed, fabricated and characterised to investigate the parameters required for a binary readout electromagnetic calorimeter. The sensors were fabricated with several enhancements in addition to standard CMOS processing. Detailed simulations and experimental results of the performance of the sensor are presented. The sensor and pixels are shown to behave in accordance with expectations and the processing enhancements are found to be essential to achieve the performance required.

A monolithic active pixel sensor for a tera-pixel ECAL at the ILC

The leading proposed technology for electromagnetic calorimeters for ILC detectors is a highly granular silicontungsten calorimeter. We have developed an active pixel sensor for such a calorimeter, which would have extremely fine granularity, allowing binary pixel readout. A first generation chip (TPAC1.0) has been fabricated, and this contains a 168x168 pixel array, consisting of 50x50 micron pixels. Each pixel has an integrated charge pre-amplifier and comparator. TPAC1.0 has been manufactured in a 0.18 micron CMOS “INMAPS” process which includes a deep pwell implant. We present recent results of the performance of the TPAC1.0 sensor together with comparison to device-level simulations.

PImMS: A self-triggered, 25ns resolution monolithic CMOS sensor for Time-of-Flight and Imaging Mass Spectrometry

In this paper, we present the Pixel Imaging Mass Spectrometry (PImMS) sensor, a pixelated Time-of-Flight (TOF) sensor for use in mass spectrometry. The device detects any event which produces a signal above a programmable threshold with a timing resolution of 25ns. Both analogue and digital readout modes are available and all pixels can be individually trimmed to improve noise performance. The pixels themselves contain analogue signal conditioning circuitry as well as complex logic totalling more than 600 transistors. This large number can be achieved without any loss of quantum efficiency thanks to the use of the patented Isolated N-well Monolithic Active Pixels (INMAPS) process. In this paper, we examine the design of the PImMS 1.0 device and its successor PImMS 2.0, a significantly enlarged sensor with several added features. We will also present some initial results from mass spectrometry experiments performed with PImMS 1.0.

Optical and x-ray characterization of two novel CMOS image sensors

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- read noise, interactive quantum efficiency of 54% at 500nm and can read a 6x6 ROI at 24,395fps. OPIC has 46±3e- 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.