S.E. Wouters

High-purity silicon soft x-ray imaging sensor array

Abstract A 256 element soft X-ray sensor array with separate x - and y -readout addresses fabricated on high-purity silicon (4kΩ cm) utilizing only standard integrated-circuit processing technologies is presented. The design of the 16 × 16 array of 250 × 250, μm 2 elements emulates that of a successful prototype. The principle of operation of the sensor is based on both the resistive and capacitive coupling of the elements in a matrix of sensing diodes. The columnar elements are resistively coupled to one output connection through the use of highly-doped polysilicon structures, while utilization of the double-layer metalization technique provides capactive coupling of those elements lying in the same row to a separate output connection. Experimental results demonstrated good sensor characteristics and confirmed two-dimensional position detection of incident radiation with minimal crosstalk.

A novel diffusion-based silicon nuclear radiation detector

Abstract This paper presents a new type of silicon nuclear radiation detector, in which the collection of generated charge carriers is established by means of diffusion instead of drift. This results in the omission of high-ohmic silicon, in a large reduction in bias voltage and in a very simple fabrication process. Calculations and experimental results demonstrate that different kinds of nuclear radiation can be detected and that a certain energy resolution can be obtained in particle measurement. The diffusion-based silicon nuclear radiation detector is well suited for counting applications, imaging and also, in the case of particles, for calorimetric measurements.

Diffusion-based silicon nuclear radiation detectors with on-chip readout circuitry

Abstract In a diffusion-based detector the generated charge carriers are collected by diffusion rather than by drift. As a result, the detector performance is reduced. However, standard substrate material is used and standard processing is applied, so that readout circuitry can be monolithically integrated on the detector. This paper describes the design and the experimental results of diffusion-based detectors in combination with on-chip readout circuitry. Both charge and current sensitive amplifiers are discussed in which the detector and the input transistor and combined into one structure, thus reducing the parasitic capacitances and increasing the packing density.

Integrating transistors on high-ohmic silicon

Abstract This paper presents a compatible technology for integrating both radiation detectors and transistors on the same high-ohmic silicon substrate. Using this technology, chips have been fabricated containing a number of test transistors (MOSFETs) with different geometries. Measurements on the devices showed a threshold voltage between 0 and -3 V, and a transconductance between 25 μA/V and 1.25 mA/V for aspect ratios between 0.7 and 50, respectively. The results demonstrate that transistors can be integrated together with radiation detectors onto one chip, which can lead to radiation detectors containing both detecting elements and signal-modification units, such as preamplifiers and multiplexers.

Compatible integration of radiation detectors and transistors

Abstract Until recently, smart nuclear radiation detectors were non-existent because of the substantial differences between the detector fabrication process and conventional IC processes. In this paper a fabrication process is presented which allows the compatible integration of both nuclear radiation detectors and (simple) MOSFET s. Test devices were fabricated containing two-dimensional nuclear radiation detectors and both polysilicon-gate and metal-gate PMOS transistors with a variety of geometries. The experimental results of the test devices show that MOS transistors can be monolithically integrated together with nuclear radiation detectors without degrading the detector quality. This opens up the way towards the development of smart nuclear radiation detectors.

Spatial resolution of a diffusion-based silicon nuclear radiation detector

Abstract The spatial resolution of a diffusion-based silicon nuclear radiation detector is investigated by analyzing the diffusion process in both vertical and lateral directions. A theoretical model is derived, which is verified by illuminating the detector from the backside with a small light bundle. The model and the measurements show good agreement and it is demonstrated that the spatial resolution mainly depends on the nuclear radiation type. For ionizing particles the spatial resolution is below 1 μm and is independent of the detector thickness. For high-energy photons the resolution depends on the absorption depth and was 310 μm for the experimental device. Although the spatial resolution for X- and γ-radiation is rather low, the diffusion-based nuclear radiation detector has an excellent position resolution for nuclear particle radiation.

Optimization of efficiency and response time of diffusion-based nuclear radiation detectors

The charge collection process in a diffusion-based silicon nuclear radiation detector was investigated by illuminating the detector at the backside with optical radiation. The results are compared to calculations and show good agreement. The collection mechanism is characterized, and the detector response to nuclear radiation and its optimum with respect to efficiency and response time are calculated. Efficiency and response time are improved by reducing the detector thickness. The lower limit of detector thickness is set by the noise level and varies for different measurement systems and applications. It is concluded that a diffusion-based nuclear radiation detector is not inherently slow and inefficient after its performance has been optimized by selecting the right detector thickness.<<ETX>>

Experimental detector chip for soft X-ray applications

Abstract In this paper an experimental chip is presented, which is made of high-ohmic silicon, containing both nuclear radiation detectors and transistors. The detectors have a two-dimensional position resolution and were fabricated according to two different multiplexing principles. The first principle is the capacitor-resistor multiplexing technique, which is superior with respect to crosstalk. The second principle is the capacitor-interconnect technique, which is superior with respect to energy measurement. The transistors were fabricated and operated under the same circumstances as the detectors and performed well. The measured parameters ( g m C gs = MHz –8 GHz ) indicate that these transistors are well suited to preamplification and multiplexing purposes. The combination of the presented detectors and transistors for soft X-ray measurement is a very good one, because the limited spatial resolution allows enough chip area for the integration of readout electronics and, when backside illumination is applied, the transistors are shielded from direct irradiation. Therefore it is concluded that the detector matrices and the transistors presented in this paper are well suited to the construction of detector matrices with on-chip signal processing for soft X-ray applications.

Sensor array with A/D conversion based on flip-flops

Abstract A RAM-compatible optical sensor array with a digital output, based on flip-flops consisting of silicon phototransistors and implanted resistors, is presented. Analog/digital conversion is realized using a triangular-wave voltage. This technique allows the construction of sensor arrays with a large number of elements.

Making radiation sensors smart enough for computers

The physical operation of nuclear radiation sensors is briefly reviewed. This is followed by a description of a typical experimental measurement-system setup, which can be divided into two parts: the application-specific part (including the detector and its associated electronics) and the computer-interfaced part (consisting of a multichannel analyzer). A number of recent improvements in the system design are discussed, followed by an extended description of one of the most promising new ideas, the monolithic integration of both the radiation sensor and its associated electronics on one high-ohmic silicon substrate. The results prove to be a stimulus for making radiation sensors smart enough for computers.<<ETX>>