Cathode Pad Research Articles

Simple Contact-Less Photo-Electrochemical (CL-PEC) Etching for AlGaN/GaN Heterostructures

AlGaN/GaN high electron mobility transistors (HEMTs) are expected to become high-frequency power devices required for next-generation communication systems because of the high breakdown voltage characteristics of GaN-based materials and the high channel density and high electron mobility of the two-dimensional electron gas (2DEG) induced at the AlGaN/GaN hetero-interface. Etching is an important process for transistors using 2DEGs at the AlGaN/GaN hetero-interface as a channel, as it provides isolation to electrically separate the neighboring devices by deep etching from the AlGaN layer to the GaN layer, and also controls the threshold voltage by the thickness of the AlGaN layer. Contactless photo-electrochemical (CL-PEC) etching is performed by immersing a sample with a cathode pad in a solution containing an oxidant and irradiating it with ultra-violet (UV) light. It is very simple set-up and is one of the most promising wet etching techniques for nitride semiconductors such as GaN [1] and AlGaN [2]. In this study, we have demonstrated the deep and shallow etching of AlGaN/GaN structures by optimizing the CL-PEC conditions.The AlGaN/GaN samples with a cathode pad were immersed into the K2S2O8-based solution, where the UV-light was irradiated to the top surface. In the CL-PEC etching, the hole concentration at the anode area to be etched and the efficiency of electron extraction at the cathode area are key parameters to control the etching rate. To demonstrate to realize both the deep and shallow etching by CL-PEC technique, the UV-light power, P in, and the ratio of the cathode area to the anode area, C/A, was changed.We have compared the etching rate of the samples having different cathode pads. The etching depth was linearly controlled by the time for the sample having a Ti/Al/Ti/Au ohmic cathode. On the other hand, the etching rate was very slow, and the etching was saturated for the sample having a Ti Schottky cathode. The results indicate that the deep and shallow etching can be switched by changing the cathode pad, where their conductivity plays an important role.The effect of changes in P in and C/A ratio on etching rate was investigated for the case of deep etching with Ti/Al/Ti/Au ohmic cathodes. The etching rate was found to be strongly dependent on P in and independent of C/A. These results suggest that the hole concentration produced by light irradiation is the dominant factor in determining the etching rate for the sample having a Ti/Al/Ti/Au ohmic cathode. We have demonstrated that such deep CL-PEC etching is useful for separating devices fabricated on AlGaN/GaN heterostructures. Evaluation of the current-voltage characteristics between two ohmic electrodes placed across the insulating region formed by CL-PEC etching showed that deep CL-PEC etching increased the resistance between the electrodes by a factor of 108. Despite being a very simple method, this is comparable to device separation by dry etching or ion implantation.The Shallow etching with a Ti Schottky cathode was then evaluated by AFM for etching depth and surface morphology after CL-PEC etching. Under optimum conditions, the etching rate of the AlGaN layer was very slow (<1.0 nm/min) and the residual thickness of the AlGaN layer could be accurately controlled. The etched surface was very smooth, with a root mean square (RMS) value of 0.4 nm for roughness. This shallow etching was applied to the gate recess fabrication of AlGaN/GaN HEMTs. The drain current-voltage (I DS-V DS) characteristics of the recess-gate HEMTs showed good pinch-off behavior, with a decrease in drain leakage current under the reverse bias and a positive shift in Vth from -3.4V (planar gate device) to 0V. The subthreshold slope (SS) values obtained from the transfer characteristics were smaller than those obtained for the planar-gate HEMTs.The CL-PEC etching enabled device separation and threshold voltage control of AlGaN/GaN HEMTs by optimizing its conditions. We believe that the CL-PEC etching is a promising alternative to dry etching and other processes that cause processing damage.Acknowledgements: This work was supported by JSPS KAKENHI- JP23K26131.

Optimisation of plasma-activated water: Plasma DBD technology and application in recirculating aquaculture system for Nile tilapia larval culture

Plasma-activated water (PAW) is a useful tool for producing pathogen-free seed fish. This study aimed to apply dielectric barrier discharge (DBD) plasma to reduce the microbial population in the water of a recirculating aquaculture system (RAS) for Nile tilapia larval culture. Initially, a PAW system prototype was developed and found to effectively reduce bacterial populations in both stagnant and circulating water. Additionally, a slight increase in water temperature was observed in the circulating water. Subsequently, the optimisation of PAW conditions in the circulating water was performed. The PAW system, with a copper anode distance of 2 cm and a 1 cm distance between the copper tip and the water surface, combined with a non-spaced cathode pad, exhibited the highest bactericidal effect. Using the optimised PAW conditions, for Experiment I, Nile tilapia larval culture was established in the RAS, supplemented with a bacterial suspension (Bacillus subtilis, Streptococcus agalactiae and Aeromonas hydrophila) to assess the bactericidal effects. Three treatments were applied: 1) control (no PAW or antibiotics), 2) PAW, and 3) antibiotic treatment for Nile tilapia larvae cultured in the RAS system for 672 h. The results demonstrated that both PAW and antibiotic treatments significantly reduced the bacterial populations in the water in relation to the control (P < 0.05). Moreover, a substantial reduction in bacterial population was observed in the whole body of the fingerlings in both the PAW and antibiotic groups in relation to the control fingerlings (P < 0.05). In Experiment II, Nile tilapia larval culture in the RAS was conducted under three different conditions: 1) control (no PAW or antibiotic), 2) PAW, and 3) antibiotic treatment, to evaluate the antimicrobial effects of PAW on waterborne bacterial populations for 672 h. Similar to Experiment I, both antibiotic and plasma treatments significantly reduced the bacterial populations in the water and whole-body fingerlings in relation to the control (P < 0.05). Notably, the growth performance and whole-body composition (moisture, crude protein, crude fat, and ash) of the fingerling fish appeared comparable among the experimental groups (P > 0.05), suggesting that PAW had no detrimental effects on long-term fish culture. Therefore, PAW can be employed to effectively reduce bacterial populations in water, thus minimising bacteria-related issues in fish without adverse impacts on fish growth.

Experimental Validation of a Novel Methodology for Electromigration Assessment in On-Chip Power Grids

A recently proposed theoretical methodology for the assessment of the electromigration (EM) induced IR-drop degradation in on-chip power/ground grids has been validated by means of measurements performed on real silicon. A voltage tapping technique was employed for the direct measurement of voltage variations at 162 nodes of the power net, stressed with 10 mA constant source current at an elevated temperature of 350 °C. A voltage drop between cathode and anode pads exceeding a specified threshold was considered as a failure. Times-to-failure (TTF) was measured on 19 packaged test grids and used for computing the mean TTF (MTTF). The EM-induced voltage degradation in this grid was also analyzed with an assessment methodology based on a simulation of stress evolution everywhere in the grid, resulting in a voiding in some of grid branches and corresponding resistance increase. A set of voiding compact models for different grid segments was developed and used in the simulations. The stochastic nature of the EM phenomenon was captured by introducing random distributions of atomic diffusivities and critical stresses across the grid and iterating them with Monte Carlo loops. A good fit between the measured voltage evolution kinetics at different grid nodes and that predicted by simulation, and the good agreement between measured and simulated failure distributions can be considered as the ever first experimental validation of this EM assessment methodology for on-chip power/ground (p/g) grids.

Design of film supported single mesa Schottky diodes for above 1THz application with submicron T-junction

A high-performance terahertz Schottky barrier diode (SBD) with a film-supported single mesa structure featuring a low structural parasitic with extremely low dielectric loss is reported in this brief. The fabricated substrate-free SBD is supported with a 2–3 µm polymer film using a low parasitic coupling capacitor of about 0.12 fF. It significantly reduces the electromagnetic coupling effect between the anode and cathode pads by 90% compared with the traditional structure of the same size. To reduce the Schottky junction capacitance at the anode, a submicron T-junction process is used with a low junction capacitance of 0.15 fF. The cutoff frequency calculated by the total capacitance of the diode is up to 4 THz. The substrate-free terahertz monolithic integration circuit based on this film-supported single mesa SBD has better performance in reducing the circuit dielectric loss, exhibiting a remarkable potential for high-frequency applications.

Fabrication of Recessed-Gate AlGaN/GaN Hemts Utilizing Contactless Photo-Electrochemical (CL-PEC) Etching

AlGaN/GaN HEMTs are promising devices to attain both high-power and high-speed switching operation for the use in next-generation power electronics circuits. From the viewpoint of fail-safe and low-power consumption design, however it is necessary to attain normally-off operation with a positive threshold voltage (V th). One of the promising approaches to attain such operation is adopting a recessed-gate structure, which can be fabricated by thinning the AlGaN layer beneath the gate electrode. We have reported the photo-electrochemical (PEC) etching process for the fabrication of the recessed-gate AlGaN/GaN HEMTs was promising to improvement of transfer characteristics of the device and control of V th[1]. In this study, we developed the contactless PEC (CL-PEC) etching process[2-5], whose experimental system was simpler than that of conventional PEC etching process, for the fabrication of the recessed-gate structure. Consequently, for the devices fabricated by CL-PEC, the etched surface was very smooth such as the as-grown surface. The device characteristics improved to be compared with those without the recessed-gate fabrication process.We used an i-Al0.24Ga0.76N (28.4 nm)/i-GaN heterostructure grown by metal organic vapor phase epitaxy on a semi-insulating SiC substrate as a sample. A Ti ohmic contact was formed on the edge of the sample as a cathode pad which was not connected to the outer circuit. The CL-PEC etching process was conducted by only dipped the sample into 0.025 M K2S2O8 aqueous solution (pH = 3.4) under illumination of UVC light, whose center wavelength was 260 nm and the intensity was 4 mW/cm2. The distance between UVC light source and the surface of sample was set to 4 cm, where the optical path in the solution was fixed at 0.5 cm. As an etching mask, the lamination film of SiN (100 nm) and photoresist was formed by sputtering and photolithography process. After the etching, TMAH treatment was conducted in recessed-gate region. An inductive-coupled-plasma reactive-ion-etching (ICP-RIE) was conducted for the device isolation. The source-drain electrodes (Ti/Al/Ti/Au), Schottky-gate and MIS-gate electrodes were fabricated by a standard evaporation process. The various devices with different gate lengths (3, 5 and 10 µm) were fabricated on the same chip. The gate width for all device was designed to be 100 μm.The etching depth and the surface morphology were evaluated by AFM technique after the CL-PEC etching. An etching rate of AlGaN layer was very slow (< 1.0 nm/min) under the optimal condition, leading to the precise control of the residual thickness of the AlGaN layer. In addition, the self-termination of the etching was observed. The etching was stopped in the AlGaN layer, leaving a thickness of 6 nm. The surface after the etching was very smooth, where the root-mean-square (RMS) value of roughness was 0.4 nm (in 7 × 7 μm2 area). The drain current-voltage (I DS-V DS) characteristics of Schottky recessed-gate HEMTs showed good pinch-off behavior. The drain leakage currents with a reverse bias decreased and the V th was shifted in the positive direction from -3.4V (planar-gate devices) to 0 V. The value of sub-threshold slope (SS), obtained from the transfer characteristics, was smaller than that obtained for the planar-gate HEMTs. In addition, the standard deviation, σ, of the V th was 5.7 mV which was much smaller than that of the planar-gate devices. These results show that the uniformity of device performance enhanced after the CL-PEC process. The MIS recessed-gate HEMTs also showed good I DS-V DS characteristics with constant saturation currents and pinch-off behavior. As similar to the Schottky HEMTs, shift of V th in the positive direction, and the improved V th uniformity were observed. In addition to this, the MIS gate structure has the advantage that the device operates under positive bias by reducing gate leakage currents. This feature is promising for increasing the drain current reduced by the recess gate structure. In conclusion, excellent electrical properties such as low-leakage currents and precise control of V th for recessed-gate AlGaN/GaN HEMTs were achieved by the low-damage CL-PEC etching with the self-terminated nature.Acknowledgements: This work was supported by JSPS KAKENHI-JP16H06421, 20H02175.[1] Y.Kumazaki et al., JJAP, 121, 184501 (2017). [2] F.Horikiri et al., APEX, 12, 031003 (2019) [3] M.Toguchi et al., APEX, 12, 066504 (2019). [4] F.Horikiri et al., IEEE Trans. Semicond. Manuf., 32, 489 (2019). [5] K.Miwa et al., APEX, 13, 026508 (2020). Figure 1

Molybdenum Capping Layer Effect on Electromigration Failure of Plasma Etched Copper Lines

Currently, chemical mechanical polishing (CMP) rather plasma etching is the most popular production process for Cu lines [1,2]. This is due to the low volatility of the copper halide, e.g., CuClx or CuBrx, at room temperature [3,4]. A plasma-based Cu etch process was invented by the authors’ group [5-7]. This process has been successfully used in fabricating ICs and TFT LCDs [8,9]. The Cu layer was converted into a CuClx or CuBrx layer in a parallel-plate plasma reaction, which was then stripped off with a HCl solution. The Cu conversion rate can be very high, e.g., 140 nm/min at room temperature. The reliability of the Cu line has been studied using the electromigration (EM) stress method [10,11]. The TiW capping layer effect on the Cu lifetime was reported [11]. In this study, the molybdenum (Mo) capping layer effect on the Cu failure process is studied. Mo/Cu and Mo/Cu/Mo stacks were deposited on the Corning glass and etched into a 4-point pattern for the EM test. All films were sputter deposited. The Mo capping and barrier layers were reactive ion etched in a PlasmaTherm 700C system at CF4/O2 10/10 sccm, 60 mTorr, 600W for 2 minutes. The Cu to CuClx conversion reaction was done in the same RIE reaction at HCl/CF4 20/5 sccm, 70mTorr, 600 W for 2 minutes. The CuClx layer was dissolved in a H2O:HCl (8:1 v/v) solution for 1 min. The Cu samples were stressed at room temperature at fixed current densities (J). Changes of line color and shape were recorded. Figure 1 shows the top view of a 30 µm wide Mo/Cu/Mo line after J = 0.6 × 106 A/cm2 stress for 10 cycles. The line broken spot occurred at the cathode or anode pad which was not observed with the TiW capped Cu line. This is because the mechanical property of the Mo film is weaker than the TiW film is [12,13]. When the probe needle was applied to the pad, a high stress was generated locally, which initiated the failure process. Figure 2(a) shows the resistance-time (R-t) curve and temperature-time (T-t) curve of a 30 μm Mo/Cu/Mo line stressed at J = 0.4 × 106 A/cm2. The resistance gradually increased with the increase of the stress time, and the resistance increased dramatically near the line broken time. The temperature of the Cu line was calculated using the JEDEC standard guidelines of JESD33-B [14]. Since the temperature increase is caused from the Joule heating effect, the T-t curve follows the same trend as that of the R-t curve. Figure 2(b) shows the top view of the Mo/Cu/Mo line at different stress time at J = 0.4 × 106 A/cm2. The original line had the sage green color. It changed to the aquamarine color with the increase of the stress time. A white region appeared before the line was broken, which became dark upon the line breakage. The color change is related to the change of the local temperature. The EM failure phenomena of the Mo/Cu and Mo/Cu/Mo lines were compared. The result will be discussed from their R-t and T-t curves as well as the color changes. The capping layer material and properties are important to the EM lifetime of the Cu line. Authors acknowledge the financial support of this work through NSF CMMI project 1633580. 1. A. Gladkikh and Y. Lereah, Appl. Phys. Lett., 66(10), 1214 (1995). 2. C. S. Hau-Riege, S. P. Hau-Riege and A. P. Marathe, J. Appl. Phys., 96(10), 5792 (2004).3. Y. Kuo and J.R. Crowe, JVST A 8(3), 1529 (1990). 4. H. Miyazaki, K. Takeda, N. Sakuma, S. Kondo, Y. Homma and K. Hinode., JVST B 15(2), 237 (1997).5. Y. Kuo and S. Lee, Jpn. J. Appl. Phys., 2(39), L188 (2000). 6. S. Lee and Y. Kuo, J. Electrochem. Soc., 148, G254 (2001). 7. Y. Kuo and S. Lee, Appl. Phys. Lett., 78, 1002 (2001). 8. Y. Kuo and S. Lee, Vacuum, 74(3-4), 473 (2004).9. J. Yang, Y. Ahn, J. Bang, W. Ryu, J. Kim, J. Kang, M. S. Yang, I. Kang, I. Cung, ECS Trans., 16(9), 13 (2008).10. C. S. Hau-Riege, Microelectronics Reliability, 44, 195 (2004).11. M. Li, J. Q. Su and Y. Kuo, 235th ECS Meeting, Abst. #120271, May 26-31 (2019).12. R. Farraro, R.B. McClellan, Metal. Trans. A, 8(10), 1563 (1977).13. A. Roshanghias, G. Khatibi, R. Pelzer and J. Steinbrenner, Surf. and Coatings Tech., 259, 386 (2014).14. EIA/JESD33-B, Standard Method of Measuring and Using the Temperature Coefficient of Resistance to Determine the Temperature of a Metallization Line (2004). Figure 1

Potential impact of bifrontal transcranial random noise stimulation (tRNS) on the semantic Stroop effect and its resting-state EEG correlates

The Stroop effect performance reflects cognitive resistance to interference. We aimed to investigate the effect of a single transcranial random noise stimulation session (tRNS) applied over the dorsolateral prefrontal cortex (DLPFC) on the semantic Stroop effect and its resting electroencephalography (EEG) correlates (β/α ratio). In a randomized, double-blind study, healthy volunteers were allocated to receive either one session of active tRNS (n=8) or one session of sham tRNS (n=11). The anode pad was placed on the scalp over the right-DLPFC and the cathode pad was placed over the left-DLPFC. A computerized adaptation of the French Stroop Color-Word Test (Victoria version) and a resting-state continuous EEG recording were administered before and after the tRNS. No significant difference were observed for either Stroop Interference/Congruent (F(1,15)=0.5, P=.5, BF=.19) or Interference/Cross (F(1,14)=3.2, P=.1, BF=0.25) ratios. No significant effect of tRNS was observed on EEG β/α ratios across electrodes (F(5,95)=0.6, P=.7, BF=0.59e-05). Under active stimulation, Pearson's tests showed significant correlations with moderate evidence between post-pre differences of Stroop Interference/Congruent and Fz-β/α ratios (r=0.88, P=.02, BF=4.05), and Stroop Interference/Crosses and Cz-β/α ratios (r=0.89, P=.008, BF=8.25), while the same correlations did not reach significance under sham conditions. We observed no significant changes in either semantic Stroop task reaction time or its EEG correlates after tRNS. However, we provide the original finding that fronto-central β/α activity becomes related to cognitive resistance to interference when the DLPFC is stimulated with random noise current. The results suggest a potential resynchronization of relevant brain frequency patterns into Stroop-related cortical involvement.

Muon physics at forward rapidity with the ALICE detector upgrade

ALICE is the experiment specifically designed to study the Quark-Gluon Plasma (QGP) in heavy-ion collisions at the CERN LHC. The ALICE detector will be upgraded during the Long Shutdown 2, planned for 2019-2020, in order to cope with the maximum interaction rate of 50 kHz of Pb-Pb collisions foreseen for Runs 3 and 4. The ambitious programme of high-precision measurements, expected for muon physics after 2020, requires an upgrade of the front-end and readout electronics of the existing Muon Spectrometer. This concerns the Cathode Pad Chambers (CPC) used for tracking and the Resistive Plate Chambers (RPC) used for triggering and for muon identification. The Muon Forward Tracker (MFT), an internal tracker added in front of the front absorber of the existing Muon Spectrometer, is also part of the ALICE detector upgrade programme. It is based on an assembly of circular planes made of Monolithic Active Pixel Sensors (MAPS), covering the pseudorapidity range 2.5 <η < 3.6. The MFT will improve present measurements and enable new ones. A selection of results from physics performance studies will be presented, together with an overview of the technical aspects of the upgrade project.

Frequency-tunable metamaterial absorber using a varactor-loaded fishnet-like resonator.

A frequency-tunable metamaterial absorber is designed with the unit cell consisting of a varactor-loaded fishnet-like resonator. This geometry allows all cathode and anode pads of the unit cells to be connected to their counterparts. Hence, only the ends of the periodic structure need to be biased, reducing the complexity of the bias network. The absorber was modeled using a full-wave simulation tool and verified experimentally with a 20×20 unit-cell prototype. Using free-space measurements, the absorber shows >90% absorption ratio from 3.96 to 5.29 GHz with a frequency tuning ratio of 28.7%, when the reverse voltage varied from 0 to 19 V.

Phase segregation, interfacial intermetallic growth and electromigration-induced failure in Cu/In–48Sn/Cu solder interconnects under current stressing

The evolution of microstructure in Cu/In–48Sn/Cu solder bump interconnects at a current density of 0.7 × 104 A/cm2 and ambient temperature of 55 °C has been investigated. During electromigration, tin (Sn) atoms migrated from cathode to anode, while indium (In) atoms migrated from anode to cathode. As a result, the segregation of the Sn-rich phase and the In-rich phase occurred. A Sn-rich layer and an In-rich layer were formed at the anode and the cathode, respectively. The accumulation rate of the Sn-rich layer was 1.98 × 10−9 cm/s. The atomic flux of Sn was calculated to be approximately 1.83 × 1013 atoms/cm2s. The product of the diffusivity and the effective charge number of Sn was determined to be approximately 3.13 × 10−10 cm2/s. The In–48Sn/Cu IMC showed a two layer structure of Cu6(Sn,In)5, adjacent to the Cu, and Cu(In,Sn)2, adjacent to the solder. Both the cathode IMC and the anode IMC thickened with increasing electromigration time. The IMC evolution during electromigration was strongly influenced by the migration of Cu atoms from cathode to anode and the accumulation of Sn-rich and In-rich layers. During electromigration, the Cu(In,Sn)2 at the cathode interface thickened significantly, with a spalling characteristic, due to the accumulation of In-rich layer and the migration of Cu atoms - while the Cu(In,Sn)2 at the anode interface reduced obviously, due to the accumulation of Sn-rich layer. The mechanism of electromigration-induced failure in Cu/In–48Sn/Cu interconnects was the cathode Cu dissolution-induced solder melt, which led to the rapid consumption of Cu in the cathode pad during liquid-state electromigration and this finally led to the failure.

Readout system of TPC/MPD NICA project

The time-projection chamber (TPC) is the main tracking detector in the MPD/NICA. The information on charge-particle tracks in the TPC is registered by the MWPG with cathode pad readout. The frontend electronics (FEE) are developed with use of modern technologies such as application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), and data transfer to a concentrator via a fast optical interface. The main parameters of the FEE are as follows: total number of channels, ~95 000; data stream from the whole TPC, 5 GB/s; low power consumption, less than 100 mW/ch; signal to noise ratio (S/N), 30; equivalent noise charge (ENC), <1000e– (Cin = 10–20 pF); and zero suppression (pad signal rejection ~90%). The article presents the status of the readout chamber construction and the data acquisition system. The results of testing FEE prototypes are presented.

Detector with a profile-based cathode and the two-coordinate pad-strip readout system

A detector with a profile-based cathode and a two-coordinate cathode readout system has been experimentally investigated. Cathode pads located in each profile along the anode wire are diagonally interconnected, thus forming strips that cross the detector at some angle with respect to the anode wire. Owing to the availability of the two cathode coordinates and the coordinate associated with the anode wire, it is possible to solve the problem of identifying high-multiplicity events in a single detector.

High voltage characteristic of large area cathode pad chambers for muon spectrometer of ALICE

Large area Cathode Pad Chambers (CPC) with inner and outer radii of 23.7 cm and 117 cm respectively have been fabricated and tested for 2nd Tracking station of Muon Spectrometer of ALICE.

Readout system of the ALICE Muon tracking detector

A Large Ion Collider Experiment (ALICE) will be aimed at studying heavy ion collisions at the extreme energy densities accessible at the CERN's Large Hadron Collider (LHC), where the formation of the Quark Gluon Plasma is expected. The ALICE muon forward spectrometer will identify muons with momentum above 4GeV/c, allowing the study of quarkonia and heavy flavors in the pseudorapidity range −4.0<η<−2.5 with 2π azimuthal coverage. The muon tracking system consists of 10 Cathode Pad Chambers (CPC) with 1.1 million of pads that represent the total number of acquisition channels to manage.In this article, we will give an overview of the ALICE Muon Spectrometer. Afterward, we will focus on tracking system Front end Electronics (FEE) and readout system. We will show that the Digital Signal Processor (DSP) architecture fulfills all the requirements, including radiation hardness against neutrons. Finally, real-time performances are discussed.

TPC cathode read-out with C-pads

A Time Projection Chamber with “C” like shaped cathode pads was built and tested. It offers a low gas gain operation, a good pulse shape and a lightweight construction. The Pad Response Function (PRF), the cathode to anode pulse height ratios and the pad pulse shapes of the C-pad structure were measured and compared with planar cathode structures in two different wire geometries. The cathode to anode signal ratio was improved from between 0.2 and 0.4 up to 0.7. The PRF was considerably improved, it has a Gaussian shape and is narrower than in the case of the planar pads. The pulse shape from the C-pad read-out is similar to the pulse shape from a detector with a cylindrical shape of electrodes. A method for aluminum pad mass production based on a precise cold forging was developed and tested.

A vertex trigger based on cylindrical multiwire proportional chambers

This article describes the technical implementation and the performance of the z-vertex trigger (CIP2k), which is part of the H1-experiment at HERA. The HERA storage ring and collider was designed to investigate electron (and positron) proton scattering at a center-of-mass energy of 320 GeV. To improve the sensitivity for detecting non-standard model physics and other high momentum transfer phenomena, the HERA ring has been ungraded between 2000 and 2003 to increase the specific luminosity for the experiments. In order to cope with the increased event and background rate the experiments were upgraded, too. The CIP2k trigger system is based on a set of five cylindrical multiwire proportional chambers with cathode pad readout, and allows to distinguish between events induced by beam background and ep-interactions at the first trigger stage. The trigger decision is calculated dead-time free with a latency of 1.5 μ s in parallel to the beam clock at 10.4 MHz. The trigger-logic is realized in large field programmable gate arrays (FPGA) using the hardware description language Verilog. The system is operational since October 2003. It suppresses background events with high efficiency and provides event timing information, as designed.

A 48 channel pulse shape digitizer with DSP

A 48 channel, 40-65 MS/sec., 10 bit pulse shape digitizer card has been designed in the VME-6U form factor. The design uses 6 octal Flash Analog to Digital Converter (FADC) chips (ADS5121 or ADS5122) from Texas Instruments. The FADCs are read out by 6 Altera Cyclone FPGAs. A 7th FPGA is used to collect and merge the event fragments. The present firmware includes trigger latency buffers, waveform segment buffers, real-time digital filtering, time stamp generation, amplitude evaluation, event formatting and buffering, plus a simple VME A24D32 interface. The design also includes a source synchronous bi-directional serial LVDS link for the interconnection of the modules to a large system. The first version of the module is designed for an R&D test readout system connected to a few hundred drift chamber cathode pads or TPC cathode/anode pads. The final version is intended for the readout of the KOPIO preradiator cathode drift chamber pads (/spl sim/75000 channels). This version will only have the LVDS interconnect. The present design using off-the- shelf commercial components is an interesting alternative to an ASIC approach for intermediate size readout system. It occupies about 3 times the area of an equivalent ASIC system, and has comparable power dissipation. In its present form, the development version of the module can be useful as a general purpose waveform digitizer and DSP with its high density (48 channels per single width VME module) at a relatively low cost per channel.

Asymmetric and double-cathode-pad wire chambers for the LHCb muon system

We present results from two types of Multi-Wire Proportional Chambers (MWPCs) with wire pitch of 1.5 mm and cathode–cathode distance of 5 mm intended for triggering purposes in the LHCb experiment. Both prototypes use cathode readout because this allows arbitrary segmentation in order to achieve the required granularity. One MWPC prototype uses a symmetric wire–cathode distance (2.5/2.5 mm) with double cathode readout, which doubles the signal compared to reading only one cathode. The second prototype uses an asymmetric wire–cathode distance (1.25/3.75 mm) with single cathode readout which also doubles the signal and in addition reduces the width of the induced charge distribution and therefore reduces the crosstalk for small cathode pads. We also performed a dedicated optimization of readout traces and guard traces in order to reduce the pad–pad crosstalk. Both prototypes show a few hundred volts of operating plateau defined as the region with 99% efficiency in a 20 ns time window. Close to the plateau end, a time resolution of better than 3 ns was achieved.

Testbeam results of a slat CPC prototype for the ALICE Dimuon Spectrometer

The ALICE Dimuon Spectrometer will measure the production of vector mesons in their muon decay mode in heavy ions collisions at the LHC in 2007. The Spectrometer includes a Tracking System, composed of 10 planes of Cathode Pad Chambers. Six larger planes (Stations 3–5) consists of several independent detectors, called slats. This poster presents the results, obtained in test beams at CERN in 2002, on a final slat of 1.20 m long.

Restoring contaminated wires, removing gas contaminants, and aging studies of drift tube chambers

The original muon detection system of the Fermilab D0 colliding beam experiment contained 12,000 drift cells 10 cm×5 cm in cross-section and up to 580 cm in length. The gas mixture used was Ar/CF 4/CO 2 (90:6:4). There was one recycling gas system for all the chambers. During the first year of operation, it was discovered that inefficient cells, all in regions of high radiation, had a contaminating shell of crud coating their wires. The source of the contaminant was outgassing of the cathode pads, which were made from a laminate of fiberglass and epoxy/polyester resin, with a copper cladding on one surface. The vapor formed a brittle sheath on the wires, but only in regions of high current discharge due to radiation from the accelerator and colliding beams. A method for cleaning wires in place was devised. By heating the wire quickly to a temperature close to the melting temperature of gold, the sheath was ripped to shreds and blown away. The procedure for “zapping” wires and for removing the contaminating vapor is presented. The upgraded D0 experiment now uses Iarocci-type mini-drift tubes for the forward muon system. The results of aging tests for these chambers are also presented.