Circuit Modification Research Articles

WE-C-342-02: The Future of Flat Panel Imagers: From Active Matrix to Active Pixel Architectures and Many Possibilities in Between

Since the turn of the century, the phrase “Flat Panel Imager” has been increasingly used in modern x-ray imaging venues ranging from large, institutional cardiac care, radiology and radiotherapy settings to community oral surgery offices. The phrase most commonly refers to those technologies employing a large area, monolithic array consisting of a two-dimensional grid of imaging pixels fabricated on a thin glass substrate. Individual pixels are made addressable by means of an “active matrix” of switches — usually, in each pixel, taking the form of a single amorphous silicon (a-Si:H) thin film transistor (TFT) coupled to some form of storage capacitor. Two variations of this relatively simple architecture (based on so-called indirect or direct detection of the incident radiation by means of a scintillator or a photoconductor, respectively) have become almost ubiquitous for a wide variety of projection (e.g. radiography, fluoroscopy, mammography) and volumetric (e.g., CBCT, tomosynthesis) imaging applications. While offering many advantages, such Active Matrix Flat Panel Imagers (AMFPIs) are restrictive in terms of signal-to-noise performance, maximum frame rate, image artifacts, configurability and cost. These limitations are inspiring considerable innovation and creativity in imager development. Some approaches involve: high-gain photoconductors such as HgI2 or avalanche-gain with a-Se (to improve system gain and DQE); active pixel circuits involving the inclusion of amplifiers in each pixel (to increase gain and DQE, frame rate, and to reduce artifacts); thick segmented scintillating converters (to increase x-ray quantum detection efficiency and DQE at megavoltage energies); flexible substrates (to provide lighter, flexible and more x-ray transparent substrates); and subtractive and additive printing of a-Si:H or organic TFTs (to reduce costs). In this talk, a broad overview of the state of conventional AMFPI technology, its limitations, the potential for improvement, and some of the avenues being pursued to achieve these improvements will be presented. In addition, challenges for some of these approaches, along with the long-term prospects for this general area of technology, will be reviewed, and the effect of large performance improvements on the practical implementation of advanced applications will be discussed. Educational Objectives: 1. Review the fundamental concepts behind the technology of flat panel imagers based on active matrix addressing. 2. Provide an understanding of the performance limitations on such active matrix, flat panel imagers (AMFPIs). 3. Outline the general approaches for achieving significant improvements over conventional AMFPI performance. 4. Detail specific improvement strategies involving front-end enhancement of converter signal and pixel level circuit modifications, which preserve the major advantages of conventional AMFPIs. 5. Discuss the long-term prospects for, and implications of flat panel imager performance improvement.

A probabilistic method to determine the minimum leakage vector for combinational designs in the presence of random PVT variations

The control of leakage power consumption is a growing design challenge for current and future CMOS circuits. Among existing techniques, ‘parking’ a circuit in a minimum leakage state during its standby mode of operation requires minimal circuit modification and results in significant leakage reduction. In this paper we present a heuristic approach (referred to as MLVC) to determine the input vector which minimizes leakage for a combinational design. This approach utilizes approximate signal probabilities of internal nodes to aid in finding the minimum leakage vector. We utilize a probabilistic heuristic to select the next gate to be processed as well as to select the best state of the selected gate. A fast SAT solver is employed to ensure the consistency of the assignments that are made in this process. A variant of MLVC, referred to as MLVC-VAR, is also presented. MLVC-VAR includes the effect of random variations in leakage values due to process, voltage and temperature (PVT) variations. Including the effect of PVT variations for determining minimum leakage vector is crucial because leakage currents have an exponential dependence on power supply, threshold voltage and temperature. To the best of the authors’ knowledge, no other minimum leakage vector determination work has to date included the effect of PVT variations. Experimental results indicate that our MLVC method has very low runtimes, with excellent accuracy compared to existing approaches. Further, the comparison of the mean and standard deviation of the circuit leakage values for MLVC with MLVC-VAR and an existing random vector generating approach proves the need for considering these variations while determining the minimum leakage vector. MLVC-VAR reports, on average, about 9.69% improvement over MLVC with similar runtimes and 5.98% improvement over the random vector generation approach with significantly lower runtimes.

Bimodal Electric Tissue Ablation-Modified Radiofrequency Ablation with a Le Veen Electrode in a Pig Model

Radiofrequency ablation (RFA) is a method of treating non-resectable liver tumors by use of a high-frequency alternating electrical current. Concerns have been raised as the local recurrence rates following treatment have been reported to be as high as 47%. The size of the ablation is limited by charring of adjacent tissues. It is hypothesized that by hydrating the liver, we can reduce charring, thus producing larger ablations, and that this can be achieved by addition of a direct electrical current to the electrical circuit. Using a pig model, standard RFA control ablations were created in the left lobe of the liver. Ablations using the modified circuit were created in the right lobe. At the end of the procedure, the pig was killed by lethal injection and the liver harvested. From the explanted liver, the diameter of each ablation was measured and the modified ablations were compared with controls using restricted maximum likelihood variance analysis. From 4 pigs, 14 controls and 12 modified ablations were produced. The mean diameter of the controls was 27.78 mm (+/- SE 3.37 mm). The mean diameter of the modified ablation was 49.55 mm (+/- SE 3.46 mm), which was significantly larger than the controls (P < 0.001). This study has shown that by modification of the standard RFA circuit with the addition of a direct electrical current, significantly larger ablations can be produced. By using this technique, the number of ablations required to treat one tumor would be less and it is anticipated this could reduce the rate of local recurrence.

Measurement Method for Imbalance Factors in Direct-Conversion Quadrature Radar Systems

In quadrature direct-conversion Doppler radar systems, the I and Q receiver channels are subject to amplitude and phase imbalance factors caused by circuit and component imperfections. This nonideality results in an undesired linear transformation of the baseband output signals which degrades output accuracy and sensitivity. With known imbalance factors, compensation can be achieved through digital signal processing, but accuracy is affected by circuit modifications required to determine those factors. Presented here is a new measurement method for I/Q imbalance factors that can be performed without significant modification to the radar system, allowing more precise imbalance correction to be achieved. A phase shifter is introduced at the receiver input to simulate a target approaching with constant velocity, resulting in sinusoidal outputs which can be easily compared to determine phase and amplitude imbalance

Gate-Level Register Relocation in Generalized Synchronous Framework for Clock Period Minimization

Under the assumption that clock can be inputted to each register at an arbitrary timing, the minimum feasible clock period can be determined if delays between registers are given. This minimum feasible clock period might be reduced by register relocation maintaining the circuit behavior and topology. In this paper, we propose a gate-level register relocation method to reduce the minimum feasible clock period. The proposed method is a greedy local circuit modification method. We prove that the proposed method achieves the clock period achieved by retiming with delay decomposition, if the delay of each element in the circuit is unique. Experiments show that the computation time of the proposed method and the number of registers of a circuit obtained by the proposed method are smaller than those obtained by the retiming method in the conventional synchronous framework.

Modification of an extracorporeal life support circuit for intraoperative correction of complex congenital heart disease

Extracorporeal life support (ECLS) was established in a newborn infant diagnosed with severe respiratory failure secondary to complex congenital heart disease. After 4 days of ECLS support in the intensive care unit, the infant was brought to the operating room for repair of the primary lesion. Due to concerns related to recurrent respiratory failure associated with blood contact to a new extracorporeal circuit, the existing ECLS circuit was modified for use in the operating room. This report describes the circuit modification steps and challenges related to running a modified ECLS circuit for cardiopulmonary support during cardiac surgery.

Testing ternary content addressable memories with active neighbourhood pattern-sensitive faults

With shrinking transistor sizes and growing transistor density, testing neighbourhood pattern-sensitive faults (NPSFs) is increasingly important for semiconductor memories. A test methodology for detecting active NPSFs (ANPSFs) and static NPSFs (SNPSFs) in ternary content addressable memories (TCAMs) is presented. March-like and two-group test methods are two commonly used testing techniques for NPSFs in random access memories. Because of the special TCAM cell structure, however, using a unique test algorithm with only either a March-like or a two-group test operations are not time-efficient. A test methodology that employs both March-based and two-group testing to cover 100% ANPSFs and SNPSFs in TCAMs is proposed. The total test complexity of the proposed test methodology is 156 N for an N×K-bit TCAM. No TCAM circuit modification is needed to support the proposed test methodology.

Surface Rippling &amp; Ion Etch Yields of Diamond Using a Focused Ion Beam: With or Without Enhanced-Chemistry, Aspect Ratio Regulates Ion Etching

Abstract The Focused Ion Beam (FIB) instrument, originally designed for semiconductor circuit modification and repair, has found considerable utility as a tool for specimen preparation in several microscopy disciplines and for micromachining small parts. Essentially, a FIB makes very small and precise cuts into a target sample, which implies well-controlled etch rates and close tolerances of surface finish. However, redeposition can affect etch rate and final surface topographies. This work quantifies this redeposition as it modifies yields for different parameters of etching; models the influence of redeposition as applicable to all ion beam processing; and optimizes FIB processing parameters for enhanced yields.

Failure analyses for debug and ramp-up of modern IC’s

Quick and successful failure analysis is a key component for in-time realization and ramp-up of new products. The structure of analysis flow from verification of failure to fault identification and corrective actions is presented with the focus on modem techniques in fault localization. For the area of design debug techniques for internal probing and circuit modification by mask less redesign are described, yield learning is demonstrated on the example of SRAM fails and scan shift loss. Finally an assessment of the future of failure analysis in this field is given.

Sample tilting technique for preventing electrostatic discharge during high-current FIB gas-assisted etching with XeF 2

FIB-induced electrostatic discharge (ESD) is a major limiting factor for achieving successful and efficient circuit modifications of LSI. We have discovered a novel antistatic technique applicable to high-current (nanoampere-order) FIB gas-assisted etching with XeF 2. The method simply utilizes inclined incidence of FIB by sample tilting. The effect of the sample tilting technique on preventing ESD was investigated using a logic LSI device fabricated by 0.13 μm technology and eight-layer copper metallization. The result demonstrated that inclined incidence of 60° prevents ESD even for high-current (12.5 nA) FIB gas-assisted etching with XeF 2. The mechanism of ESD suppression by the sample tilting technique was proposed by taking account of the presence of processing gas molecules and the tilting-angle dependences of ion range, back-scattering yield, secondary-electron yield and etching rate. In the case of FIB irradiation at inclined incidence with XeF 2 gas flow, more secondary-electrons and sputtered particles are ejected with higher energies than those for the case of normal incidence. This leads the ionization probabilities of neutral gases and the sputtered particles to be increased, and results in producing increased low-energy electrons around the FIB processing area. These low-energy electrons suppress the FIB-induced positive charging.

Novel charge neutralization techniques applicable to wide current range of FIB processing in FIB-SEM combined system

FIB-induced charging is one of the most critical issues for achieving successful circuit modifications of LSI. We have developed novel charge neutralization techniques applicable to a wide current range (from pico to nanoampere-order) of FIB processing in a FIB-SEM combined system. The method utilizes a 500 eV focused electron beam instead of an electron shower, and also a combination of microprobing and FIB-assisted deposition to make a current path from FIB processing point to the grounded microprobe. The effects of our techniques on charge neutralization capability were investigated using electrically erasable-programmable read-only memory devices and n-MOS transistors. For the low FIB current condition of less than 500 pA, it is found that the focused electron beam prevents threshold voltage shifts of both irradiated and neighboring transistors, and that the ratio of electron to ion beam currents is a key parameter to achieving effective charge neutralization. We also demonstrated that the combined method of microprobing and FIB-assisted deposition prevents parameter shifts of transistors even for high-current (nanoampere-order) FIB irradiation. Moreover, we evaluated the upper-limit resistance of the current path formed by FIB-assisted carbon deposition to prevent charging induced by a given FIB current.

Anticoagulation during extracorporeal life support

Extracorporeal life support is a modified form of cardiopulmonary bypass used in patients with respiratory and/or cardiac failure in whom conventional therapy has failed and it is believed that the underlying organ dysfunction is reversible. During the provision of extracorporeal life support there is continuous contact between circulating blood and the foreign surfaces of the extracorporeal circuit. This exposure of blood to non-biologic surfaces initiates a complex inflammatory response which includes activation of procoagulant mechanisms. Anticoagulation is used in an effort to prevent thrombosis in the extracorporeal circuit. Despite attempts to balance procoagulant and anticoagulant activity, both bleeding complications and thrombosis do occur. Heparin is the most common anticoagulant used in extracorporeal support. Unfortunately, there are a number of shortcomings of heparin anticoagulation and the available methods to monitor heparin activity, particularly so in infants and children. There are a number of novel anticoagulants and anticoagulant strategies on the horizon including surface modification of the extracorporeal circuit which will hopefully lead to limitation of both bleeding and thrombotic complications in patients receiving extracorporeal life support.

A New Self-Converging System with Combination of Magnetic Lens and Uniform Horizontal Deflection Field for Color CRTs

Color CRTs (Cathode Ray Tubes) are still evolving in competition with other display devices in the growing TV markets, with continuing demands for enhanced performance and lower cost. In response to these trends, we have developed a new self-converging system of CRT with simple structure. It offers advantages in terms of high resolution for HDTV and large deflection angle for short depth TV sets. The system realizes less spot distortion at the screen periphery of the CRT and lower horizontal dynamic focus voltage than those in a conventional self-converging system, while keeping the cost just as low. In the system, a uniform horizontal deflection field and a newly-developed magnet lens are utilized. The uniform field reduces the spot distortion in exchange for occurrences of raster distortion and convergence error, both of which can be corrected by the newly-developed magnet lens without additional circuit modifications. As a core part of the new system, the lens power of the newly-developed magnet lens varies along the horizontal axis in order to simultaneously achieve convergence and correct the pincushion distortion of the raster. Furthermore, countermeasures for magnet-related issues are taken from the viewpoints of real operation and mass production. The system with the new DY was evaluated in experiments using 86cm CRTs (16:9), and it has been found that the system realizes substantially smaller spot distortions as well as favorable convergence and raster performances, with a drawback of decrease in horizontal deflection sensitivity. The spot oblateness, defined as horizontal spot diameter divided by vertical spot diameter, has decreased from 2.65 to 1.70 accompanying a 15% reduction of horizontal spot sizes at the comers of the screen with 30% decreased dynamic focus voltages and 10% decreased horizontal deflection sensitivity.

Repeated cocaine exposure in vivo facilitates LTP induction in midbrain dopamine neurons

Drugs of abuse are known to cause persistent modification of neural circuits, leading to addictive behaviours. Changes in synaptic plasticity in dopamine neurons of the ventral tegmental area (VTA) may contribute to circuit modification induced by many drugs of abuse, including cocaine. Here we report that, following repeated exposure to cocaine in vivo, excitatory synapses to rat VTA dopamine neurons become highly susceptible to the induction of long-term potentiation (LTP) by correlated pre- and postsynaptic activity. This facilitated LTP induction is caused by cocaine-induced reduction of GABA(A) (gamma-aminobutyric acid) receptor-mediated inhibition of these dopamine neurons. In midbrain slices from rats treated with saline or a single dose of cocaine, LTP could not be induced in VTA dopamine neurons unless GABA-mediated inhibition was reduced by bicuculline or picrotoxin. However, LTP became readily inducible in slices from rats treated repeatedly with cocaine; this LTP induction was prevented by enhancing GABA-mediated inhibition using diazepam. Furthermore, repeated cocaine exposure reduced the amplitude of GABA-mediated synaptic currents and increased the probability of spike initiation in VTA dopamine neurons. This cocaine-induced enhancement of synaptic plasticity in the VTA may be important for the formation of drug-associated memory.

Current multiplier to improve generator-to-load coupling for pulse-power generators

The load inductance, Ld, can be several times smaller than that of the pulsed power generator, L0, limiting the energy transfer efficiency. We define a relatively simple circuit modification, which improves the generator-to-load coupling, multiplying the load current in the case of interest, where L0⪢Ld. The suggested circuit modification operates similarly to an N:1 transformer and it can be designed to operate in vacuum with pulsed-power loads at high currents (many megaamperes). The current multiplier requires an additional volume having high self inductance, L, connected through convolutes to the generator and load. In its simplest configuration, N=2, a single convolute is required. The presented analysis shows that the efficiency of the proposed current multiplication scheme can theoretically exceed the values for a typical direct load-to-generator circuit. The modified hardware allows an increase of the load current by the factor of Id∕Ig=NL∕(L+Ld), where Ig represents the generator current and L can be easily made much greater than Ld either with or without the use of magnetic cores. The only uncertainties of this approach are potential convolute losses and the slight increase in load current rise time. Preliminary experimental tests were performed with a scaled down configuration which demonstrated current gain of 1.7 in the frequency range of interest and showed good agreement between analytically predicted and measured currents. The benefit of the scheme is also illustrated by simple circuit simulations for two types of potential applications requiring high power densities in vacuum: isentropic compression studies with Ld=constant loads, and imploding z-pinch research with dynamic [Ld(t)] loads. The proposed device is applicable for improving the characteristics of existing and future pulse power facilities.

Construction of a pulmonary artery pump for unifocalization and repair of pulmonary atresia with ventricular septal defect and major aortopulmonary collaterals

Single-stage repair has been presented as the treatment of choice for pulmonary atresia with ventricular septal defect and major aortopulmonary collaterals. This surgical approach may result in the difficult decision of whether to close the ventricular septal defect. This decision may significantly affect the postoperative course of the patient. There are several diagnostic techniques clinicians may use to help them decide if closure is indicated. One technique is to modify an extracorporeal circuit to deliver precise flow rates of blood into the newly created pulmonary arterial system, at the same time supporting the patient during the operative procedure. While this technique is not novel, there is only a single published description of the circuit. This report is brief and does not discuss potential complications that these modifications may cause. Therefore, it is the purpose of this paper to describe a circuit modification to perform this diagnostic measurement as well as elucidating potential risks of this technique.

Gas delivery and virtual process chamber concept for gas-assisted material processing in a focused ion beam system

Gas-assisted etching and material deposition using gaseous precursors have become a critical part of integrated circuit modification and other applications of focused ion beam (FIB) systems. Widely used methods of gas injection in FIB systems are either needle-type or shroud-type gas delivery nozzles. Each of these methods of gas delivery has significant drawbacks. Release of the gas from the needle-type nozzles is detrimental for the vacuum level in the main chamber of the system, as the gas quickly dissipates from the process area. Insertion of shroud concentrators into the primary ion beam path and the path of secondary electrons leads to a significant decline in the signal-to-noise ratio of the FIB image. Proposed “CUPOLA” geometry of the gas delivery nozzle could allow one to effectively concentrate process gas in the area of interest, as is currently done by shroud concentrators, and, according to secondary-electron trajectory simulations, would significantly improve the signal level of the secondary-electron image, as compared to the shroud concentrators.

Failure Analysis Turned Upside Down: A Review of Backside Analysis Techniques

Abstract This article provides a high-level review of the tools and techniques used for backside analysis. It discusses the use of laser scanning and conventional microscopy, liquid and solid immersion lenses, photon emission microscopy (PEM), and laser-based fault isolation methods with emphasis on light-induced voltage alteration (LIVA). It explains how laser voltage probing is used for backside waveform acquisition and describes backside sample preparation and deprocessing techniques including parallel polishing and milling, laser chemical etching, and FIB circuit edit and modification.

Development of void-free focused ion beam-assisted metal deposition process for subhalf-micrometer high aspect ratio vias

Low resistance metal deposition in deep submicron vias is required for circuit rewiring in focused ion beam (FIB)-based integrated circuit modification. Voids in high aspect ratio deposition, associated with the application of traditional FIB process to tungsten deposition in vias with aspect ratios beyond 10:1 contribute substantially to the resistance of the via. Pinch off of the via aperture is frequently observed. The dynamics of tungsten deposition within vias was studied through a series of via cross sections with variable deposition dose, and revealed accelerated deposition growth on the walls at the top of the vias. Accelerated deposition on the sidewalls, where the primary beam interacts with the substrate at a glancing angle, suggested that the deposition growth is initiated by secondary charged particles generated at the point of primary beam impact rather than by the primary beam itself. The results are in agreement with mechanisms previously proposed and confirmed by experiments. In order to prevent the generation of secondary particles on the walls of the via, and the consequent pinch off closure of the via aperture, confining the primary beam to an area much smaller than the aperture of the via was attempted. With this process, secondary particles are generated at the bottom of the via and trapped within the via, which was expected to lead to bottom-up deposition growth. A dose series study of the deposition produced by the proposed process confirmed the uniform growth of the tungsten fill from the bottom of the via. Void-free depositions were made in 5 μm deep vias ranging in size from 0.5 μm by 0.5 μm to 0.2 μm by 0.2 μm, corresponding to aspect ratios from 10:1 to 25:1, respectively.

The long-term potential of LTP.

Long-term potentiation has captured the attention of neuroscientists for over two decades. It has provided motivation to investigate the detailed mechanisms of synaptic transmission and remains a prime candidate for mediating circuit modifications during development and experience-dependent plasticity. However, much remains to be learned about this fascinating phenomenon, which will certainly continue to entice neuroscientists throughout the twenty-first century.