Dummy Cell Research Articles

Characterization of a Wireless Potentiostat for Integration With a Novel Implantable Biotransducer

Wireless potentiostats are being developed and commercialized for use in the development of implantable electrochemical biosensors for the monitoring of physiological markers in a wide range of pathologies. The merits and drawbacks of the Pinnacle 8151 dual potentiostat were investigated for use with a novel implantable biotransducer, the dual responsive microdisc electrode array (MDEA 5037) of ABTECH Scientific. The potentiostat was evaluated with R and RC dummy cells and with MDEA transducers modified with polypyrrole-poly(2-hydroxyethyl methacrylate) electroconductive hydrogels that were all qualified by calibrated ac impedance spectroscopy. In a laboratory setting, the 8151 potentiostat maintained a steady and unbroken signal as far away as 75 ft (23 m), and when unobstructed, up to 100 ft (30 m). The error between the two channels was determined to be 6.4 (±0.3)% and 0.7 (±0.1)% for resistor-capacitor dummy cells ( RC=nominally 10 MΩ and 1 μF) and resistor dummy cells (R=nominally 10 MΩ), respectively. The intra-channel variability was judged to be too large for exacting analyte determinations.

Reliability of electrochemical noise measurements: Results of round-robin testing on electrochemical noise

Sixteen laboratories have performed electrochemical noise (EN) measurements based on two systems. The first uses a series of dummy cells consisting of a “star” arrangement of resistors in order to validate the EN measurement equipment and determine its baseline noise performance, while the second system, based on a previous round-robin in the literature, examines the corrosion of aluminium in three environments. All participants used the same measurement protocol and the data reporting and analysis were performed with automatic procedures to avoid errors. The measurement instruments used in the various laboratories include commercial general-purpose potentiostats and custom-built EN systems. The measurements on dummy cells have demonstrated that few systems are capable of achieving instrument noise levels comparable to the thermal noise of the resistors, because of its low level. However, it is of greater concern that some of the instruments exhibited significant artefacts in the measured data, mostly because of the absence of anti-aliasing filters in the equipment or because the way it is used. The measurements on the aluminium samples involve a much higher source noise level during pitting corrosion, and most (though not all) instruments were able to make reliable measurements. However, during passivation, the low level of noise could be measured by very few systems. The round-robin testing has clearly shown that improvements are necessary in the choice of EN measurement equipment and settings and in the way to validate EN data measured. The results emphasise the need to validate measurement systems by using dummy cells and the need to check systematically that the noise of the electrochemical cell to be measured is significantly higher than the instrument noise measured with dummy cells of similar impedance.

Performance of an Anode Supported Solid Oxide Fuel Cell with Indirect Internal Reforming

The conversion of fuel into hydrogen-rich gas is necessary for fuel cells. This can be achieved either indirectly in fuel processing systems, in which the hydrocarbon feed is converted in an external catalytic steam reformer, or directly in the fuel cell. In this paper, the unit module of solid oxide fuel cell was assembled by one reformer and four cells. The reformer was fabricated by extruded dummy cell and combined with two cells on each side respectively. The reforming catalyst was coated on internal channel of the dummy cell. The unit module has successfully tested with wet CH4 as fuel and air as oxidant and its maximum power density exceeded 150 mW/cm2 at 750 ºC.

Nonlinear Analysis: The Intermodulated Differential Immittance Spectroscopy

Intermodulation is used for the analysis of the nonlinear behavior of electrochemical and electronic systems. As a matter of fact, different than the passive elements, electrochemical systems have a highly nonlinear character, which can be used to obtain information on the reaction mechanism and structure of the double layer. The setup for measuring and analyzing the intermodulated sidebands is discussed in detail, using a commercial Schottky diode as the ideal system. A general intermodulated differential immitance spectroscopy technique was consequently defined as the analysis of the variation of the immittance elements as a function of the stimulus frequency, and its transfer function was called differential immittance spectrum. Through a simple model, it was possible to precisely calculate the flat band voltage and the doping level of the Schottky diode from a single differential immittance spectrum. The differential immitance spectra of a dummy cell containing passive elements demonstrated the resolution limits of the technique.

조화 전류 측정에 의한 분극 저항 평가

Harmonic current was measured for a dummy cell with various values of resistance, and the procedure developed through the measurements was applied to the investigation of effects of the amplitude of applied frequency and applied potential on the harmonic current of a stainless steel and a carbon steel in chloride containing solutions. From the measurements of harmonic current in the dummy cell, the optimum values of applied frequency and applied potential in harmonic current measurements were found to be 1 mHz and 20 mV (or lower), respectively. Increase in harmonic current with applied frequency was observed in the case where the level of harmonic current is low as in a stainless steel. Decrease in polarization resistance was also noted in this corrosion system with either increasing applied frequency or decreasing applied potential. However, no obvious effects of applied frequency was observed on harmonic current and polarization resistance in a carbon steel in which the level of harmonic current is high.

Importance of 4-tert-Butylpyridine in Electrolyte for Dye-Sensitized Solar Cells Employing SnO2 Electrode

The photovoltaic performance of dye-sensitized solar cells (DSSCs) employing SnO2 electrodes was investigated while increasing the content of 4-tert-butylpyridine (TBP) in the conventional liquid-type electrolyte. As the added TBP content increased, the open circuit voltage (Voc) and conversion efficiency were highly enhanced while the short circuit current (Jsc) was not much affected. With the electrolyte of 2.0 M TBP, the Voc and conversion efficiency were increased by 26 and 33%, respectively, compared with the conventional electrolyte (0.5 M TBP). The electrochemical impedance spectra revealed that the enhancement of Voc resulted from the negative shift of the SnO2 conduction band potential and the increase in resistance of electron recombination by 1 order of magnitude. It is noteworthy that the optimized concentration of TBP for the SnO2 electrode is greatly larger than that for the TiO2 electrode. This may be due to the much faster electron recombination rate and more positive conduction band potential of the SnO2 electrode. The SnO2 electrode modified with TiO2 shell showed only slightly enhanced performance due to the similar effects of shell layer and those of the TBP. In contrast to the SnO2, TiO2 electrodes did not show performance enhancement with the electrolyte of TBP concentration larger than 0.5 M. The impedance spectra of symmetric dummy cells employing Pt counter electrodes indicated that the catalytic effect of Pt was deteriorated, and the resistance of electrolyte diffusion was increased by the higher concentration of TBP. This brings up the need for development of a counter electrode that TBP is not easily adsorbed on, and alternative additives to TBP which are not highly viscous.

Using single transients on the performance analysis of electrochemical noise amplifiers

The acquisition of electrochemical noise is always connected with the question of appropriate measuring devices. The noise measurement system shall allow to process the apparent fluctuations in an electrochemical cell in the low millivolt or microampere range and to record them without any changes. The measurement amplifier is an essential part of the measurement system, but its behavior in the chain of signal processing is difficult to define by a corrosion expert. The present article shows possibilities for the determination of the performance of a noise measurement amplifier. A dummy cell model is often used to get a realistic approach to the sources of electrochemical noise. This article introduces a model describing the generation of single transients from the basic electrochemical corrosion reactions. The model determines fluctuations in the potential which can be measured as voltage fluctuations on a real dummy cell circuit. With the help of a special arbitrary signal generator, artificial noise transients based on this description are applied to a commercial noise measurement system. The acquired signals are compared with the original signals from the signal source and the influences of the noise amplifier on the signals are discussed.

Current mapping of a proton exchange membrane fuel cell with a segmented current collector during the gas starvation and shutdown processes

Current distribution during the gas starvation and shutdown processes is investigated in a proton exchange membrane fuel cell with an active area of 184 cm2. The cell features a segmented cathode current collector. The response characteristics of the segmented single cell under different degrees of hydrogen and air starvation are explored. The current responses of the segment cells at different positions under a dummy load in the shutdown process are reported for various operating conditions, such as different dummy loads, cell temperatures, and gas humidities under no back pressure. The results show that applying a dummy load during the cell shutdown process can quickly reduce the cell potential and thereby avoid the performance degradation caused by high potentials. The currents of all the segment cells decrease with time, but the rate of decrease varies with the segment cell positions. The rate for the segment cells near the gas outlet is much higher than that of the segment cells near the gas inlet. The current of the segment cells decreases much more quickly at a lower gas humidity and high temperature. This study provides insights in the development of mitigation strategies for the degradation caused by starvation and shutdown process.

Improvement of the mechanical durability of micro porous layer in a proton exchange membrane fuel cell by elimination of surface cracks

In this study, gas diffusion layers (GDLs) for proton exchange membrane fuel cell (PEMFC) were subjected to accelerated stress tests to investigate the progression of mechanical degradation of micro porous layers (MPLs) over a short period of time, and crack-free MPL was prepared to enhance the mechanical durability of the MPL. A dummy cell was designed for the mechanical degradation of MPLs. There was no catalyst layer in the dummy cell and only air was supplied into the dummy cell to avoid electrochemical degradation of the MPL. In the MPL degradation experiments, several puddle-shape defects were formed only around the cracks in the surface of the MPL, and these defects negatively affected the performance of the PEMFC. The single cell performance dramatically decreased at a high current density due to the puddle-shape defects. Thus, crack-free MPL was manufactured to reduce mechanical damage on the surface of MPL by adding a water-soluble polymer binder to the MPL slurry. The puddle-shape defects were not detected on the surface of the home-made crack-free MPL, and the decrease in the single cell performance after mechanical degradation of MPL was insignificant when the home-made crack-free MPL was used in the cathode.

An Embedded DRAM Technology for High-Performance NAND Flash Memories

An embedded DRAM using a standard NAND flash memory process has been demonstrated for the first time. This embedded DRAM without extra costly manufacturing process realizes 2.4 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{2}$</tex> </formula> /Mb macro density and provides large-capacity on-chip page buffers and data caches for NAND flash memories to enhance their performances. A 32 KB DRAM buffer macro with 1.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\hbox{m}}^{2}$</tex> </formula> cell has been fabricated with a 32 nm NAND flash memory process. Even with small 3 fF cell using a planar MOS capacitor, an enough <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\pm}$</tex></formula> 100 mV cell signal has been obtained by introducing a technique to self-boost cell node up to 4 V using a merit of high-voltage NAND flash process, and two techniques to curtail parasitic bitline capacitance down to 60 fF at 128 wordlines per bitline. An undershoot problem of cell nodes due to unwanted plateline bounce is resolved by a two-step-rise/fall wordline scheme. Installation of dummy cell scheme to obtain a half of “1” data (not an average of “1” and “0” data) cuts out 32 KB macro size by 1.3% while suppressing mismatch to 3 mV at the grounded bitline precharge. The 32 KB test vehicle shows 90 ns random cycle time with 15 ns burst cycle time (66 Mb/s/pin). The measured characteristics of 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,{\hbox{10}}^{-18}$</tex> </formula> bit error rater (BER) by soft error and 10 ms data retention at 85 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,^{\circ}{\hbox{C}}$</tex> </formula> are enough for page buffer application in a NAND flash memory. The measured active current of 32 KB macro is 7 mA at 90 ns random cycle, but only 3.2 mA at practical use of 15 ns burst with 256B page access.

Generation of Accurate Reference Current for Data Sensing in High-Density Memories by Averaging Multiple Pairs of Dummy Cells

Methods to generate an accurate reference current by averaging multi-pair dummy cells' currents for distinguishing the data in sense amplifiers (S/As) of a large scale memory with resistance change cell is presented and analyzed. The predicted characteristics are confirmed by comparing them with measurement results of the functionalities and the retention time distributions in a floating body random access memory (FBRAM). The methods are found to be especially effective in situations where signals are seriously degraded such as in sensing the signals of tail bit cells in retention time distributions, making the retention time performance of the FBRAM improved drastically. The sense amplifiers which can accommodate the dummy cell averaging methods are identified to find a necessary condition for a S/A to afford the methods.

An Enhanced Canary-Based System With BIST for SRAM Standby Power Reduction

To achieve aggressive standby power reduction for static random access memory (SRAM), we have previously proposed a closed-loop V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> scaling system with canary replicas that can track global variations. In this paper, we propose several techniques to enhance the efficiency of this system for more advanced technologies. Adding dummy cells around the canary cell improves the tracking of systematic variations. A new canary circuit avoids the possibility that a canary cell may never fail because it resets into its more stable data pattern. A built-in self-test (BIST) block incorporates self-calibration of SRAM minimum standby <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> and the initial failure threshold due to intrinsic mismatch. Measurements from a new 45 nm test chip further demonstrate the function of the canary cells in smaller technology and show that adding dummy cells reduces the variation of the canary cell.

A Self-Timed SRAM Design for Average-Case Performance

This paper presents a self-timed SRAM system employing new memory segment technique that divides memory cell arrays into multiple regions based on its latency, not the size of the memory cell array. This is the main difference between the proposed memory segmentation technique and the conventional method. Consequently, the proposed method provides a more efficient way to reduce the memory access time. We also proposed an architecture of dummy cell and completion signal generator for the handshaking protocol. We synthesized a 8MB SRAM system consisting of 16 512K memory blocks using Hynix 0.35-µm CMOS process. Our implantation shows 15% higher performance compared to the other systems. Our implementation results shows a trade-off between the area overhead and the performance for the number of memory segmentation.

Guideline for an assessment of electrochemical noise measurement devices

AbstractPro‐active ageing management is becoming more and more important for the economical and safe operation of industrial plants. A key element for a pro‐active ageing management approach is to apply in situ corrosion monitoring. The electrochemical noise (EN) technique is an example of a promising method, especially for monitoring localised corrosion phenomena. Currently, research work on the EN technique is carried out in several laboratories worldwide for different kind of industrial applications but also for the investigation of corrosion mechanisms. A prerequisite for performing serious research on the EN measurement technique is a careful evaluation of the measuring system, even if commercially available EN measurement instruments are used. Therefore, testing on well‐defined dummy cells should always be a preliminary step to assess the baseline noise of the EN measurement equipment and to ensure data validity. For this purpose a guideline has been developed by the European Cooperative Group on Corrosion Monitoring of Nuclear Materials (ECG‐COMON 1) as an outcome from round‐robin testing on EN. The current guideline describes a simple procedure for the performance and evaluation of EN measurement equipment using dummy cells.

A High Measurement Channel Density Impedance Array Analyzer: Instrumentation and Implementation Approaches

The development of impedance-based array devices is hindered by a lack of robust platforms and methods upon which to evaluate and interrogate sensors. One aspect to be addressed is the development of measurement-time efficient techniques for broadband impedance spectroscopy of large electrode arrays. The objective of this work was to substantially increase the throughput capability of low frequency impedance measurement of a large channel-count array analyzer by developing true parallel measurement methods. The goal was achieved by Fourier transform based analysis of simultaneously-acquired, multi-channel, time-based, current and voltage data. Efficacy and quantitative analysis of the parallel approach is demonstrated through complex impedance measurement of dummy cell arrays consisting of up to 100 elements to sub-Hertz frequencies. The accuracy and measurement-time efficiency of the standard sequential measurement method, and a hybrid standard + parallel approach, are evaluated.

Characterization of Nonlinear Background Components in Voltammetry by Use of Large Amplitude Periodic Perturbations and Fourier Transform Analysis

Under most experimental conditions, a distinctly nonlinear background current is encountered in all forms of voltammetry which arises from the potential dependence of the capacitance. The nonlinear background current has been successfully modeled under large amplitude sinusoidal ac voltammetric conditions with a fourth order polynomial. The model was applied to a dummy cell containing a nonideal ceramic capacitor and commonly used electrodes. The nonlinearity in behavior of the background capacitance is particularly significant when considering the discrimination between the Faradaic and background contributions in the higher order harmonics resolved in ac voltammetry by Fourier transform-inverse Fourier transform approaches and in the simulation of the background current and hence double-layer capacitance as a function of potential. Typically, measurable background current under large amplitude conditions is detectable in the dc and fundamental to fourth harmonic components in large amplitude ac voltammetry. For analytical purposes, this background current can be corrected on a per harmonic basis without the need for any model. Background correction has been successfully applied to the first four harmonics for the oxidation of ferrocenemonocarboxylic acid over the concentration range of 5-500 microM in aqueous 0.5 M NaCl solution.

Dynamic Electrochemical Impedance Spectroscopy

The hardware and software for a dynamic electrochemical impedance spectroscopy system are described. The applied waveform is a continuous computer-generated multisine waveform added to a potential sweep. A fast potentiostat applies the potential signal and the impedance is derived from the Fourier transforms of the measured current and potential responses. Impedance spectra are available continuously around the cyclic voltammogram. The quality and limitations of the system are investigated with several dummy cells

Comparison of Corrosion Rate Measurement of Copper, Zinc, and C1018 Steel Using Electrochemical Frequency Modulation and Traditional Methods

Abstract Experimental aspects of making corrosion rate measurements with the electrochemical frequency modulation technique (EFM) have been discussed. Corrosion rate and corrosion kinetic parameters can be obtained without prior knowledge of the Tafel slopes. Several cases were considered using a dummy cell designed to mimic a corrosion reaction. These approaches were then applied to copper, zinc, and carbon steel samples and the results were compared to more traditional electrochemical techniques like polarization resistance and electrochemical impedance spectroscopy. Good agreement has been observed between traditional methods and EFM.

Wide $V_{\rm DD}$ Embedded Asynchronous SRAM With Dual-Mode Self-Timed Technique for Dynamic Voltage Systems

Voltage-dependent timing skews in precharge and sensing activities cause functional failure and reduce the speed of asynchronous static random-access memory (SRAM). Data-dependent bitline-leakage current further increases the timing skews and reduces the yield of asynchronous SRAM. A dual-mode self-timed (DMST) technique is developed for asynchronous SRAM to eliminate the timing-skew-induced failures and speed overhead across various process, voltage, and temperature conditions. The DMST technique employs a single replica column and new dummy cells to track both precharge and sensing activities in asynchronous SRAM, with bitline leakage considered. The DMST-technique simulation uses both 65-nm and 0.35-mum technologies. Several 0.35-mum DMST SRAM macros were fabricated in a test chip and embedded in a mass-produced system-on-a-chip suitable for various battery/supply-voltage configurations. Measurements demonstrated that the DMST technique can be operated continuously over a wide range of supply voltages, from 39.4% to 151.5% (or 212.1%, given device durability) of the nominal supply voltage (3.3 V). The fabricated macros also confirmed that the DMST technique is scalable for various bitline lengths and offers the same area overhead as conventional sense-tracking-only replica-column schemes.

Hydrogen and Stress-Induced De-lamination in an IrO2 Layer of Ferroelectric Random Access Memories

During the device lifetime tests such as high temperature operational life (HTOL) and high temperature storage (HTS) tests, a physical de-lamination of the IrO2 layer in vertical conjunction to pulsed plate-line, so-called here additional top electrode (ATE), ATE has appeared and localized in specific cell arrays. This failure stems either from the reduction of IrO2 by the penetrated hydrogen at the interface between ATE Ir to top electrode (TE) Ir or from lack of dummy cells applied, or both. In the back end of line (BEOL), several heat treatments were introduced and then the reduction was reduced. It is essential to consider a deliberated anneal procedure in the BEOL integration. This is because otherwise case may provoke a contact failure in pulsed plate-line node of cell arrays. Also, we simulate stress distribution in cell arrays depending on how many dummy cells have been taken into account. The fluctuation of the stress projected on the IrO2 layer should be controlled uniformly by adding a certain number dummy cells.