Changes In Device Parameters Research Articles

Perturbation Theory for Solar Cell Efficiency I—Basic Principles

A streamlined method of calculating the sensitivity of a solar cell's current and maximum power to small changes in device parameters is proposed. The method also introduces three sensitivity factors related to the effects of changes in the generation, bulk, and surface recombination rates on the maximum power, which are amenable to spatial plots in a device simulator. The analysis is rigorous to first order and generally applicable to multidimensional solar cells with injection-level-dependent lifetimes and surface recombination velocities, with or without “photon recycling,” under low injection level conditions at the maximum power point.

Effects of Scatter Radiation on ICD and CRT Function

Effects of direct radiation on implantable cardiac devices have been well studied. However, the effects of scatter radiation are not as clear. Recommendations on management of patients with implantable cardiac devices undergoing radiotherapy are based on limited studies mostly involving pacemakers. We sought to elucidate the effects of scatter radiation on implantable cardioverter-defibrillators (ICDs) and cardiac resynchronization therapy (CRT)-ICDs. We exposed 12 ICDs and eight CRT-ICDs to 400 cGy of scatter radiation from a 6-MV photon beam. Devices were programmed with nominal parameters and interrogated prior to radiation, after each fraction, upon completion of the radiation course and again 1 week later. A retrospective review of patients undergoing radiotherapy at the Mayo Clinic-Rochester between 2002 and 2007 in whom the device was outside the radiation field was also performed. There were 13 patients with devices undergoing radiotherapy during this time period, 12 of whom were interrogated prior to and after radiation. Interrogation reports were reviewed for device reset or parameter changes. There was no evidence of reset or malfunction during or after radiation. Also, no episodes of device reset, inappropriate sensing or therapy, or changes in programmed parameters were found in our review of patients undergoing radiotherapy. Device reset or malfunction associated with scatter radiation likely represents an unpredictable, rare occurrence. While we see no clear contraindication to radiotherapy in patients with ICDs or CRT-ICDs, precautions should be taken to avoid direct radiation exposure and to closely evaluate patient outcomes before and after the radiation course.

Interface Fermi Level Pinning at Contacts Between PEDOT: PSS and Molecular Organic Semiconductors

Photoemission studies of interfaces between molecular organic semiconductors and the conducting polymer PEDOT:PSS [mixture of PEDOT (poly-3,4-ethylenedioxy-thiophene) and PSS (polystyrenesulfonate)] demonstrate that it is impossible to control the charge injection barriers at such contacts by either a systematic change of the work function of the conducting polymer or that of the organic semiconductor. Instead, these interfaces are, in all cases, characterized by a charge transfer across the interface and a resulting Fermi level pinning. Thus interfacial charge barriers do not explain observed changes in device parameters as a function of the work function of the polymer electrode.

LETTERS/COMMENTARY

At the “Second International Workshop on Seizure Prediction” held recently in Washington, DC, under the co-sponsorship of NIH/NINDS and the AES, the importance of prospectively comparing the therapeutic efficacy of “closed-” vs. “open-loop” brain electrical stimulation was identified as an important research aim, and the meaning of these terms was briefly debated. Therapies that utilize any type of feedback, including patient seizure diaries, are “closed-loop”. The term “open-loop” was adopted for description of clinical trials with devices lacking automated means for (a) detecting seizures, quantifying their severity, and logging these data; and (b) triggering delivery of therapy based on seizure detections. As currently used, the term “open loop” may create confusion since the therapies to which it is applied rely on patient diary-feedback. The following clarification may be useful: Closed-loop therapy: Any therapy that uses a feedback loop. The feedback may be real-time or delayed (off-line); for both these options, the feedback may be automated or manual, objective or subjective, and may be used to trigger therapy delivery or to adjust parameters or dose. Open-loop therapy: Any therapy that operates without any feedback loop. Recent trials that use automated seizure detection to trigger electrical stimulation directly to the brain (Osorio et al., 2005; Bergey et al., 2006) are examples of automated real-time closed-loop. One of these trials (Osorio et al., 2005) provides real-time automated therapy delivery and objective quantitative assessment of response, while the other (Bergey et al., 2006) provides only automated therapy (as assessment is based on seizure diaries). Vagus nerve stimulation with the neurocybernetic prosthesis (Cyberonics, Houston, TX, U.S.A.), exemplifies two closed-loop modalities: (1) real-time manual closed loop, when the magnet is used to activate the generator in response to an “aura”; and (2) delayed closed loop, when device parameter changes are based upon subjective feedback in the form of seizure diaries. With these definitions in place, the incorrectly stated and irrelevant/futile aim of comparing “open-loop” vs. “closed-loop” therapies should be re-framed. With respect to brain stimulation studies, we offer the following formulation: The aim is to compare efficacy (and adverse events) of therapies that use either continuous, periodic, or random brain electrical stimulation to that of therapies based on contingent stimulation (i.e., in response to) seizure detections. This would be a worthwhile endeavor that should be pursued using objective and quantifiable assessment means such as seizure detection algorithms, instead of patient seizure diaries; diaries are inherently and grossly inaccurate (Blum et al., 1996), provide information only about seizures with clinical manifestations (a small fraction of all recorded seizures) (Osorio et al., 2002), and do not quantify intensity, duration, and extent of spread.

Cardiac Pacemakers and Implantable Cardioverter Defibrillators: In Vitro Magnetic Resonance Imaging Evaluation at 1.5-Tesla

To evaluate the effect of Magnetic Resonance Imaging (MRI) performed at 1.5-Tesla on current generation pacemakers and ICDs to identify safe parameters for MRI examinations. Pacemakers (Identity ADx XL DR+ 5386 and Identity ADx DR + 5380 generators; 1688T/52-cm atrial and ventricular leads) and ICDs (Atlas + V-243, Epic + V-236, and Epic + HF V-350 generators; Riata 1581/65-cm and QuickSite 1056K/75-cm leads; St. Jude Medical, Sylmar, California, USA) were evaluated for magnetic field interactions. MRI-related heating was assessed using various levels of RF power (SARs) and conditions that included scans on different body regions. Functional aspects of the devices were evaluated immediately before and after MRI procedures utilizing nine different pulse sequences. Induced currents were measured using a custom built system. Magnetic field interactions will not create a hazard for these pacemakers and ICDs. All scans of the "head" and "lumbar" regions resulted in temperature changes < or =0.5 degrees C at SARs ranging from 2.0 to 3.0-W/kg. For the "chest" area, temperature increases ranged from 0.4 degrees C to 3.6 degrees C at an SAR of 2.0-W/kg. No memory corruption, hardware changes, or changes in device parameters were seen. Magnetic field gradients have a low likelihood of inducing currents that would stimulate the heart. No hazardous magnetic field interactions or physiologically significant heating occurred for certain conditions. There was no permanent effect on device function. By following specific conditions, these pacemakers and ICDs may be safe for patients scanned at 1.5-Tesla.

Fabrication of Microcrystalline Cubic Silicon Carbide/Crystalline Silicon Heterojunction Solar Cell by Hot Wire Chemical Vapor Deposition

The n-type microcrystalline cubic silicon carbide (µc-3C–SiC:H) films were deposited by hot wire chemical vapor deposition (HWCVD) at a low substrate temperature (∼300 °C). Heterojunction silicon based photovoltaic devices were fabricated by depositing wide band gap n-type µc-3C–SiC thin films on p-type Si wafers, whose thickness and resistivity were 200 µm and 1–10 Ω cm, respectively. The silicon wafers were textured using alkaline etchant prior to the device fabrication. The photovoltaic parameters of a typical device were found to be Voc=560 mV, Jsc=35.0 mA/cm2, fill factor (F.F.) = 0.724, and η=14.20%. Numerical analysis was performed using automat for simulation of hetero structures (AFORS-HET), a one-dimensional device simulators to determine the probable cause of the changes in device parameters before and after the ageing of the filament.

751 Is it clinically worthy to optimise CRT device programmation? A mid-term follow up study in patients with heart failure and LBBB

pacemakers, ICDs and bi-ventricular ICDs. Methods: Devices included Identity ADx XL DR 5386, Identity ADx DR 5380, Atlas V-243, EpicTM V-236, EpicTM HF V-350, 1688T/ 52-cm atrial and ventricular leads, Riata 1581/65cm high voltage lead, and QuickSite 1056K/75cm left ventricular (LV) lead from St. Jude Medical, Sylmar, CA. Devices were evaluated for magnetic field interactions (force and torque). MRI-related heating was assessed with guidance from ASTM F2182 using various levels of RF power and imaging conditions that included scans on different body regions. Each system was placed in a gelled-saline-filled, head/torso phantom to simulate typical clinical placements and temperatures were recorded using fluoroptic probes. Functional aspects of the devices in DOO and DDD were evaluated immediately before and after MRI was performed utilizing nine different pulse sequences. Imaging artifacts were characterized using T1-weighted and gradient echo pulse sequences. Results: All scans of the “head” and “lumbar” regions resulted in temperature increases less than or equal to 0.5C at SAR (Specific Absorption Rate) levels of 2.0 3.0 W/kg. The temperature increase ranged from 0.4 C 3.6 C at a SAR of 2.0 W/kg when scanning the “chest” region, with a maximumum increase of 0.9 C at the LV tip and 3.6 C at the ICD lead tip in the RVOT. No memory corruption, hardware changes, or changes in device parameters were seen. Oversensing was observed at the most sensitive device settings when programmed to DDD during some of the MRI scans with totally normal function at all other times. Device function was unaffected in DOO. The magnetically induced displacement force was no greater than 0.05 N for the pacemakers and 1.6 N for ICDs. Image artifacts were substantial for the pulse generators and minor for the leads. Conclusion: No physiologically significant heating or magnetic field interactions were observed in the tests performed. There was no permanent effect on the device function. These findings have important implications for patients with these devices and are consistent with recent published articles.

Structural and dielectric properties of Sb-doped PLZT ceramics

Lead Zirconate Titanate (PZT), a member of ABO 3 (A = mono or divalent, B = tri to pentavalent ions) family is a solid solution of lead titanate and lead zirconate ceramics. PZT ceramics with compositions near Morphotropic Phase Boundary (MPB) offer good ferroelectric, piezoelectric and electrical properties. It is well established that the substitution of La 3+ at the Pb site of PZT (PLZT) gives improved optoelectronic and piezoelectric properties of the materials. In most of the complex PLZT compounds (by increasing the La content in Zr or Ti rich compounds) broadened dielectric peaks or diffuse phase transitions with relaxation character in the transition temperature have been observed. For better understanding of the diffuse phase transition on double doping at the Pb site of PLZT near the MPB and the changes in physical or device parameters, we have carried out systematic studies on structural and dielectric properties of the compounds. In this paper, we report the study of the effect of paired dopants (La and Si) in PZT ceramics. Samples of Sb-doped PLZT were synthesized by high-temperature solid-state solution reaction technique. Preliminary crystal structure and microstructure of the compounds were studied by X-ray diffraction technique. Detailed dielectric studies of the samples suggest that they undergo ferroelectric paraelectric diffuse phase transition. Temperature dependence of dc resistivity of the compounds exhibits Negative Temperature Coefficient Resistance behavior.

An improved method to estimate intrinsic small signal parameters of a gaas mesfet from measured dc characteristics

This investigation offers a technique to predict the ac behavior of mm wavelength GaAs metal semiconductor field effect transistors by using dc characteristics. To predict the intrinsic equivalent circuit parameters of the device from dc data, the measured dc characteristics are first simulated by employing a nonlinear dc model. The effects of biasing on the device ac parameters are evaluated for its low-noise applications. An improvement greater than 10% in predicting the ac response of the device is observed. The concept of depletion layer modification caused by the transverse electric field inside the channel is introduced for accurate Miller's capacitor modeling. It is assumed that with increased device biasing there are more unbalanced positive charges in the gate depletion toward the drain-side of the Schottky barrier. The electric field lines originated by these uncompensated charges induce an opposite charge density in the gate electrode. This modifies the gate biasing and hence the Schottky barrier depletion. As a result, the values of intrinsic ac device parameters change. It is observed that an accurate dc modeling is key to predicting an accurate ac small signal equivalent circuit of a device.

Study of the electrical performance of chip-on-board (COB) devices

When a bare die is flipped directly onto the printed circuit board (PCB) during chip-on-board assembly, it becomes exposed to a number of factors, which could influence its electrical performance. Although the mechanical integrity of flip-chip devices has been thoroughly studied, there is very little evidence of detailed investigations of the electrical performance of these devices. The present paper aims to bridge this gap by studying the electrical parameters of flip chip devices and analysing the changes occurring following assembly. A dedicated test chip comprised of passive and active semiconductor devices was designed for the study. Two different types of tacky flux and underfill materials were used in the flip chip assembly process. The flip chip structures were then subjected to various environmental stress techniques for accelerating ageing. Electrical parameters of the devices such as threshold voltage, I-V characteristics, off-state leakage current, current gain, and resistance were measured at various stages of the programme. A slight change in device parameters was observed immediately after assembly. Further change in some device parameters was observed after environmental stressing. The paper investigates the mechanisms that could be responsible for the changes, such as mechanical stresses introduced during the flip chip process or ionic contamination inherent to the assembly process.

Analyzing the mechanism of hydrogen adsorption effects on diamond based MIS hydrogen sensors

The current conduction mechanism and the change in device parameters of diamond based MIS hydrogen sensor upon hydrogen adsorption is investigated over the temperature range of 27–100°C. The current conduction mechanism of the diamond based hydrogen sensitive MIS diode in the forward-bias region is found to be space charge limited in air and hydrogen environments. The space charge limited current (SCLC) conduction mechanism is characterized by an ohmic region at low bias voltage and a power law dependency of voltage ( I- V n with n ≥ 2) at higher voltage range. The space charge limited current (SCLC) conduction mechanism prohibits the use of conventional methods to determine the device parameters. This paper presents a methanol to determine device parameters such as the ideality factor, n, barrier height, φ B, and tunneling factor, aχ 1 2 δ , and explain the change in these parameter upon H 2 adsorption.

Radiation effects on the Viking-2 preamplifier-readout chip

We have studied the radiation sensitivity of the Viking-2 VLSI circuit which has been designed for the readout of silicon strip detectors and manufactured at Mietec in 1.5 μm CMOS technology. Both biased and unbiased chips have been irradiated with a 137Cs γ source up to a total dose of 2 kGy (200 krad) after which all tested chips were still fully functional. We report the characteristic changes of device parameters with dose, including equivalent noise charge for different capacitive loads, and determine transistor threshold shifts and change of mobilities.

Device parameter changes caused by manufacturing fluctuations of deep submicron MOSFET's

The effects of typical manufacturing fluctuations upon four electrical device parameters: threshold voltage, transconductance, substrate current and off current have been studied for deep submicron MOSFET's (0.1 /spl mu/m). The analysis reveals that the electrical parameter sensitivity in deep submicron devices differs from micron size devices, making a revision of the validity of conventional semiconductor manufacturing heuristics for future technology mandatory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the investigation of degradation mechanisms in ultrahigh performance GaAs heterojunction bipolar transistors

Recently, current-induced degradation in the form of V/sub BE/ shifts has been reported when the heterojunction is stressed under high-level forward current injection. Although the V/sub BE/ shift is an indication of device parameter change, the degradation mechanisms cannot be readily identified. An approach is presented that uncovers the device degradation mechanisms by measuring the inverted mode I/sub C/ at room temperature and the forward mode I/sub B/ at low temperature. The correlation between the change in the inverted I/sub C/ and an anomalous component (tunneling current) of I/sub B/ is observed and attributed to beryllium interstitial diffusion into substitutional sites.

Circuit related issues due to radiation in hostile environments

Various types of radiation in hostile environments cause transient and permanent changes in the devices used in complex integrated circuits. The failure of a particular IC is a function not only of the basic material and device parameter changes but also of the circuit environment in which the device is located. Circuit techniques have been developed which minimize the detrimental effects of radiation on certain types of circuits. In other cases, circuit techniques are not very effective in minimizing radiation effects. This work discusses selected issues related to the interactions between device radiation effects and circuit performance or circuit failure in a hostile radiation environment. This is not meant to be a comprehensive study of circuit effects but rather several examples are selected to illustrate the issues involved in designing circuits to operate in hostile radiation environments.

Effect of diffusion and modulated frequency in an ion-implanted OPFET

Studies have been made on the effect of diffusion and modulated frequencies in an ion-implanted Si photo MESFET (OPFET). It is observed that for a particular radiation flux density and absorption coefficient, the device characteristics ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> ), threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> ), and intrinsic device parameters (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</inf> ,Ras <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</inf> , etc.) change only at millimeter-wave frequencies. When the effect of diffusion is ignored, the modulated frequency alone also changes these terminal properties of the OP-FET at millimeter-wave frequencies, but then the changes are more prominent. The diffusion simply reduces these effects.

A Packaged 20-GHz 1-W GaAs MESFET with a Novel Via-Hole Plated Heat Sink Structure

A novel Via-Hole plated heat sink (PHS) structure with an improved gate-packing density is developed for K-band GaAs power FET's. The gate-packing density in this structure is increased to four times greater than that in the conventional direct via-hole structure, by making via-holes under the source-grounding pads fabricated outside the FET active area. The increase in the gate-packing density allows the design of a high-power, high-frequency FET with a larger gate periphery. The resultant 2.4-mm gate periphery device with 0.7µm gate length delivered 1.1 W (30.4 dBm) of output power with 5.0-dB gain and 19.2-percent power added efficiency at 20 GHz, and exhibited 0.74 W (28.7 dBm) at 30 GHz. The same type of device assembled in the hermetically sealed package delivered 1.0 W (30 dBm) of output power with 4.8-dB gain and 13-percent power added efficiency at 20 GHz. Thermal and mechanical-environmental tests were made to assess the reliability of the novel Via-Hole PHS FET. Results showed no failure nor significant change in device parameters throughout the tests.

UHF ultra low noise cryogenic FET preamplifier

A design is presented for a stable liquid helium cooled 430 MHz preamplifier, using a GaAs MESFET, with a 3 dB bandwidth of 35 MHz. Changes in device parameters with temperature are considered. Accurate matching is achieved by the use of GaAs varactor diodes and may be optimised in situ by controlling the bias voltages. The expected improvements in performance from both the increase in transconductance, and the decrease in the level of the Johnson noise sources is observed. By this technique the authors have achieved a noise temperature TN<or approximately=10K with a single stage gain of 19 dB. The output power for 1 dB gain compression is +7 dB m.

Proposed process modifications for dynamic bipolar memory to reduce emitter-base leakage current

One of the requirements of the dynamic bipolar memory cell is low junction leakage currents. Performance considerations, especially those of peripheral circuitry, may require that the memory is fabricated with the process commonly used in the fabrication of high-performance logic circuits, in which As emitters are used, and in which base surface concentrations are high. It is shown here that because of this, devices fabricated with this process have high emitter-to-base leakage current due to a presence of the tunneling component. It is further shown that this tunneling component can be reduced by simple modifications of the performance-oriented process. The experimental data presented here also show the observed changes in device parameters with various process modifications, which can be helpful in drawing a balance between a performance and leakage current requirements.

Proposed Process Modifications for Dynamic Bipolar Memory to Reduce Emitter-Base Leakage Current

One of the requirements of the dynamic bipolar memory cell is low junction leakage currents. Performance considerations, especially those of peripheral circuitry, may require that the memory is fabricated with the process commonly used in the fabrication of high-performance logic circuits, in which As emitters are used, and in which base surface concentrations are high. It is shown here that because of this, devices fabricated with this process have high emitter-to-base leakage current due to a presence of the tunneling component. It is further shown that this tunneling component can be reduced by simple modifications of the performance-oriented process. The experimental data presented here also show the observed changes in device parameters with various process modifications, which can be helpful in drawing a balance between performance and leakage current requirements.