Sudeep Chatterji

A new approach to the optimal design of multiple field-limiting ring structures

In this paper, a computer-based analysis is performed to study layout solutions aimed at increasing the breakdown voltage in Si-microstrip detectors. For optimum performance it is crucial to achieve maximum breakdown voltage for Si detectors operating at very high bias due to the extremely hostile radiation environment of next generation experiments such as LHC. The performance of Si-microstrip detectors can be improved by implementing floating field-limiting rings around the active detector area. A simulation study has been carried out to evaluate the distribution of breakdown voltage as a function of guard-ring spacing (GS). The purpose of this work is to find a criterion to optimize GS for multiple ring structures incorporating various physical and geometrical parameters as an aid to design optimization. Using this criterion the optimum spacing of guard rings for multiple ring structures was obtained. The proposed criterion is very robust and is insensitive to the number of guard rings, junction depth and radiation damage. The simulation results for the seven-ring design agree well with experimental measurements.

Analysis of interstrip capacitance of Si microstrip detector using simulation approach

Abstract The harsh radiation environment in future high energy physics experiments like large hadron collider provides a challenging task to the performance of Si microstrip detectors. The performance of Si microstrip detectors is scaled in terms of the breakdown performance of the device while having no adverse effect on signal/noise ratio (S/N). The adoption of overhanging metal electrode is known to limit the breakdown risks in high voltage biased microstrip detectors. The present study aims at investigating the effect of width of overhanging metal electrode on the interstrip capacitance, and hence on noise performance of silicon microstrip detectors to be used in the Preshower detector of the electromagnetic calorimeter at compact muon solenoid. The influence of various geometrical and physical parameters like strip-width/pitch ratio of the strips, surface state fixed oxide charge and relative permittivity of the passivant on the interstrip capacitance of Si detectors is also discussed. The adoption of limited overhanging metal electrode is shown to have positive impact on interstrip capacitance while improving the breakdown performance of the device also.

Simulation study of irradiated Si sensors equipped with metal-overhang for applications in LHC environment

The performance of metal-overhang (MO) equipped silicon micro-strip sensors, after irradiation for the preshower detector to be used in compact muon solenoid (CMS)experiment at the large hadron collider (LHC), CERN, has been studied through simulations. Detailed calculations using Hamburg model have allowed the parameterization of these effects and helped to simulate the operation scenario of MO equipped sensors over ten years of LHC operation. The utility of overhanging metal extension as junction termination technique after space charge sign inversion (SCSI) has been explored in detail for the first time in this work. Several interesting results like a shift in the optimal oxide thickness in MO equipped structures after irradiation have been reported. The comparison of dielectric and semi-insulator passivated MO equipped structures after irradiation has been studied. Also, the impact of various crucial geometrical parameters like device depth (W/sub N/), width of back N/sup +/ layer used for ohmic contact (W/sub N//sup +/), strip width (W), strip pitch (P) and width of overhang extension (W/sub MO/) on the MO equipped structure after SCSI has been presented in detail.

Analysis and Comparison of the Breakdown Performance of Semi-Insulator and Dielectric Passivated Si Strip Detectors

Abstract The harsh radiation environment in future high-energy physics (HEP) experiments like LHC provides a challenging task to the performance of Si microstrip detectors. Normal operating condition for silicon detectors in HEP experiments are in most cases not as favourable as for experiments in nuclear physics. In HEP experiments the detector may be exposed to moisture and other adverse atmospheric environment. It is therefore utmost important to protect the sensitive surfaces against such poisonous effects. These instabilities can be nearly eliminated and the performance of Si detectors can be improved by implementing suitably passivated metal-overhang structures. This paper presents the influence of the relative permittivity of the passivant on the breakdown performance of the Si detectors using computer simulations. The semi-insulator and the dielectric passivated metal-overhang structures are compared under optimal conditions. The influence of various parameters such as passivation layer thickness, junction depth, metal-overhang width, device depth, substrate resistivity and fixed oxide charge on the junction breakdown voltage of these structures is extensively studied. The results presented in this work clearly demonstrate the superiority of the metal-overhang structure design employing semi-insulator passivated structures over dielectric passivated ones in realising a given breakdown voltage. The effect of bulk damage caused by hadron environment in the passivated Si detectors is simulated, to a first order approximation, by varying effective carrier concentration (calculated using Hamburg Model) and minority carrier lifetime. This approach allows getting an insight of the device behaviour after radiation damage by evaluating the electric field distribution, and thus proves helpful in predicting some interesting results.

A CAD investigation of metal-overhang on multiple guard ring design for high voltage operation of Si sensors

The extension of Si detectors to the next generation high-energy physics experiments such as large hadron collider implies a reliable operation in high radiation environment which is by far the main technological challenge for these detectors. Multiple field limiting ring systems are well established as a means of protecting diffused junction from high voltage premature breakdown. Also, a spread of the Al metallization over the inter-cathodic field oxide sensibly lowers the electric field at the junction edges, thus, allowing for higher breakdown voltages. The purpose of this work is to combine the positive aspects of these two termination techniques with the aim of defining layouts and technological solutions suitable for the use of Si detectors in adverse radiation environment. An important feature is the potential distribution in the multi-guard ring structure, which depends on the bulk doping concentration, the oxide charge, the size of the gap between guard rings and the metal-overhang design. A systematic investigation on the breakdown performance is done by varying the physical and geometrical parameters such as width of overhang, guard ring spacing, junction depth and oxide charge. CAD tools are used for evaluating potential and electric field distributions within the device.

Two-dimensional breakdown voltage analysis and optimal design of a silicon microstrip detector passivated by a dielectric

In this paper, we present a two-dimensional computer-based analysis. We study extensively the influence of various parameters, such as the permittivity of the passivant dielectric, the passivation layer thickness, the junction depth, the n-layer thickness and the fixed oxide charge, on the breakdown voltage of the dielectric passivated silicon microstrip detector. The relative permittivity of the passivant dielectric layer deposited over the oxide influences the breakdown voltage once some minimum value of passivation layer thickness has been reached. The breakdown voltage of shallow junction devices remains nearly constant over a wide variation in passivation layer thickness. It is shown that, for deeper junction devices, the breakdown voltage remains almost constant up to a particular passivant layer thickness and then increases sharply. The effects of device depth and fixed oxide charge on the passivated device are also analysed. Based on this T-CAD simulation, we propose a layout for a detector protection structure with optimized performance. The design presently envisaged offers decisive advantages over a number of possible alternatives in silicon detector technology. We have found good agreement between previous experimental data and the simulation results.

Impact of field limiting ring technique on breakdown voltage of irradiated Si sensors

The very intense radiation environment of high luminosity future colliding beam experiments (like LHC) makes radiation hardness the most important issue for Si detectors. One of the central issues concerning all LHC experiments is the breakdown performance of these detectors. The major macroscopic effect of radiation damage in determining the viability of long-term operation of Si sensors is the change in effective charge carrier concentration (N/sub eff/), leading to type-inversion. Floating field limiting guard rings have been established as means of improving the breakdown performance of Si detectors. In this work the usefulness of the guard rings in improving the breakdown performance of detectors after type-inversion has been studied. Simulations are carried out to study the effect of change in N/sub eff/ on the breakdown performance of optimized guard ring structure using two dimensional device simulation program, TMA-MEDICI. Detailed calculations using Hamburg Model have allowed the parameterization of these effects to simulate the operation scenario of Si detectors over 10 years of LHC operation.

Impact of metal overhang and guard ring techniques on breakdown voltage of Si strip sensors - 2003 IEEE nuclear science symposium, medical imaging conference, and workshop of room-temperature semiconductor detectors

The importance of Si sensors in high-energy physics (HEP) experiments can hardly be overemphasized. However, the high luminosity and the high radiation level in the future HEP experiments, like Large Hadron Collider (LHC), has posed a serious challenge to the fabrication of Si detectors. For the safe operation over the full LHC lifetime, detectors are required to sustain very high voltage operation, well exceeding the bias voltage needed to full deplete the heavily irradiated Si sensors. Thus, the main effort in the development of Si sensors is concentrated on a design that avoids p-n junction breakdown at operational biases. Among various proposed techniques, Field-limiting Ring (FLR) (or guard ring) and Metal-Overhang (MO) are technologically simple and are suitable for vertical devices. Since high-voltage planar Si junctions are of great importance in the HEP experiments, it is very interesting to compare these two aforementioned techniques for achieving the maximum breakdown voltage under optimal conditions. In the present work, the breakdown performance of metal-overhang and field-limiting ring techniques is compared for various values of junction depth and fixed oxide charge under similar conditions using two dimensional device simulation program TMA-MEDICI.

Performance Characteristics of Semi‐Insulator‐ and Dielectric‐Passivated Si Strip Detectors

The harsh radiation environment in present and future high-energy physics experiments, such as the Large Hadron Collider (LHC), is a driving force for the development of high-voltage Si strip detectors. It is well known that mobile surface ions can affect the stability and long-term behaviour of Si detectors. These instabilities can be nearly eliminated and the performance of Si detectors can be improved by implementing suitably passivated metal-overhang structures. This paper presents the influence of the relative permittivity of the passivant on the breakdown performance of the Si detectors using computer simulations. The semi-insulator and the dielectric-passivated metal-overhang structures are compared under optimal conditions. Influence of the salient design parameters such as field oxide thickness, junction depth, metal-overhang width, and the surface charge on the breakdown performance of these structures are systematically analyzed, thus providing a comprehensive picture of the behaviour of metal-overhang structures and helping in the detector optimization task. The results presented in this paper clearly demonstrate the superiority of the metal-overhang structure design employing semi-insulator-passivated structures over dielectric-passivated ones in realizing a given breakdown voltage.