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A discharging circuit with high energy efficiency is designed for supercapacitors. In this design, the capacitors are connected in parallel during charging and connected in series during discharging. With this method, the voltage of the capacitors in series becomes two times larger during discharging; thus, the step-down circuit can be used to produce the desired output voltage. The efficiency of the step-down circuit is four times larger than that of the step-up circuit in simulations. The experimental results agree well with the theoretical values. These results show that a step-down circuit is superior to a step-up circuit for extracting electrical energy from supercapacitors. [ABSTRACT FROM AUTHOR]

This paper considers the energy consumed by charging and discharging a width-variable capacitor. The capacitor with plate distance d is coupled with repulsive mechanical potential energy, which is proportional to 1/dn. In this capacitor model, there is a stable point between attractive electrical force and repulsive mechanical force. All energies, including the electrostatic energy, potential energy, and energy dissipation, are proportional not to the ordinary value V2 but to V2/(n-1)+2, where V is the abrupt power supply voltage. We apply N-stepwise adiabatic charging to the width-variable capacitor system. It is shown that the energy consumption after charging and discharging (or recycling) can be 1/N times smaller than that of the conventional abrupt operation. By increasing the step number N, the adiabatic operation can ideally charge and discharge the width-variable capacitor system with absolutely no energy dissipation, although the voltage dependence of energies is quite different from the usual one. Adiabatic charging is very promising for realizing dissipationless operation in the proposed system. [ABSTRACT FROM AUTHOR]

A circuit for adiabatically charging and discharging a supercapacitor was designed. A microprocessor sets the duty ratio of the switching transistors that control the inductor current. Changing the duty ratio in a stepwise fashion causes the output voltage to change in a similar fashion. Stepwise voltage changes enable adiabatic charging and discharging. Current measurements showed that the eight-step charging and discharging of a supercapacitor reduced the energy dissipation to one-eighth of that for a constant-voltage process. The circuit enables precise voltage control in small steps. [ABSTRACT FROM AUTHOR]

This paper describes characteristics of stepwise adiabatic charging with an inductor current by controlling switching transistors. An exact analytical resolution is obtained by using a vector comprising a voltage and a current. From a matrix calculation, the voltage and current can be written with solutions of the characteristic equation, power supply voltage, the switching ratio in the switching transistor circuit, and the number of switchings. Using the expression, the voltage and current in the stepwise adiabatic charging method can be derived clearly. As a result, it is clarified analytically that, in N-step charging, the current is reduced to 1/N so that the energy dissipation is reduced to 1/N. Next, the experimental switching transistor circuit with the controller is described, which is composed of discrete ICs. The experimental inductor current in the circuit is investigated. The measured current is reduced to 1/N in N-step charging, which is consistent with the simulated one from the theory. It is also confirmed experimentally from the average power supply current that power consumption is reduced to 1/N. [ABSTRACT FROM AUTHOR]

A single-bit-line (BL) static RAM (SRAM) circuit that employs adiabatic charging of a word line during a read operation was found to provide a large dynamic noise margin (DNM) for reading. Single-BL reading is achieved by using a left access transistor and a shared reading port. The shared reading port greatly reduces the BL capacitance, enabling the voltage of the BL connected to the low-voltage node of the flip-flop to change from the precharge voltage to GND. An analysis of the time-wise change in DNM revealed that the read noise margin of this circuit was 1.9 times larger than that of a conventional two-BL circuit. This circuit enables the design of an SRAM that is smaller than a conventional one, resulting in lower energy consumption. [ABSTRACT FROM PUBLISHER]

Abstract: Thin film Al2O3/Al-rich Al2O3/SiO2 structures were fabricated on p-Si substrates. Radio-frequency magnetron co-sputtering was used to form Al-rich Al2O3 thin film as the charge-trapping layer of nonvolatile Al2O3 memory. Capacitance–voltage measurements showed a large hysteresis due to charge trapping in the Al-rich Al2O3 layer. The charge trap density was estimated to be 42.7×1018 cm−3, which is the largest value ever reported for an Al-rich Al2O3 layer; it is six times larger than that of a conventional metal–nitride–oxide–silicon memory. Thermal annealing was found to reduce the leakage current of the Al2O3 blocking layer, thereby providing this structure with better data retention at room temperature than an as-deposited one. In addition, the annealed structure was found to exhibit good data retention even at 100°C. [Copyright &y& Elsevier]

Abstract: A thin-film structure comprising Al2O3/Al-rich Al2O3/SiO2 was fabricated on Si substrate. We used radio-frequency magnetron co-sputtering with Al metal plates set on an Al2O3 target to fabricate the Al-rich Al2O3 thin film, which is used as a charge storage layer for nonvolatile Al2O3 memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance–voltage (C–V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al–O capacitor structure, we clarified experimentally that the maximum capacitance in the C–V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al2O3 is increased, a large charge trap density is obtained. When the Al content in the Al–O is changed from 40 to 58%, the charge trap density increases from 0 to 18×1018 cm −3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory. [Copyright &y& Elsevier]

Four definitions of static random access memory (SRAM) cell write margins (WMs) were reexamined by analyzing the dependence of the WM on the SRAM cell transistor threshold voltages (Vth's) in order to find a preferable definition. The WM is expected to obey the normal distribution if the differential coefficients of the WM to Vth's are constant over a wide range of Vth variations. This means that the write yield can be easily predicted by a small number of measured samples. Using SPICE in 45-nm technology, we examined which definition had Vth linearity, as well as giving an accurate write limit. The distribution predicted from the linearity was verified by the Monte Carlo simulation. As a result, the definition proposed by Gierczynski was found to be the most suitable definition for predicting the distribution and the write yield. [ABSTRACT FROM PUBLISHER]

Radio-frequency magnetron cosputtering by setting an Al metal plate on an Al2O3 target is an effective method for fabricating Al-rich Al2O3 thin film, which is used as a charge storage layer for nonvolatile Al2O3 memory. The wet etching rate of the fabricated AlO film increases with Al content. The optical transmittance decreases when the Al content in AlO increases. Using rf magnetron cosputtering, the authors fabricated an Al2O3 film with an embedded Al-rich Al2O3 and investigated the charge trapping characteristics after a 30 min annealing at 550 °C. C-V characteristics indicate that the Al-rich Al2O3 structure is very stable after annealing. The charge trap density in Al-rich Al2O3 after annealing is much larger than that in stoichiometric Al2O3. [ABSTRACT FROM AUTHOR]

This letter describes the capacitance-voltage (C-V) characteristics of a new nonvolatile Al2O3 memory with nanoscale thin film deposited by electron-cyclotron-resonance sputtering. Al-rich Al2O3 was fabricated at a reduced oxygen gas flow rate and used as a charge storage layer of the Al2O3 memory, which is located between the tunnel insulator and blocking insulator. C-V characteristics show a large hysteresis window due to the Al-rich structure, but there is no hysteresis window in the case of stoichiometric Al2O3 structure. This memory will stay nonvolatile for several years or more. The number of electrons injected into the insulator in the case of nanoscale memory cell length is discussed. A discussion of the statistical Gaussian distribution indicates that about 50 localization sites are necessary in Al2O3 memory with 10 nm cell length for realizing a 1.8 V change of the threshold voltage, which corresponds to the control of ten electrons in the insulator. This structure is easily achieved by the proposed Al-rich Al2O3 memory. [ABSTRACT FROM AUTHOR]

The charging efficiency of a lithium-ion capacitor (LIC) is an important problem. Until now, due to the stepwise charging method, the charging efficiency of 95.5% has been realized. However, the problem is that the issue of what level the charging efficiency can be increased to, is yet to be well investigated. In this article, the problem is investigated under the galvanostatic charging condition. The charging efficiency is measured as a function of the charging current. As a result, it can be more than 99.5% when the charging is quasi-static, in other words, an adiabatic process is realized. Next, the problem of how much energy can be taken out from the energy-stored capacitor is investigated with a load resistor circuit. It is clarified that the discharging energy from the capacitor is equal to the stored energy in the case when a load resistor is used and the discharging is quasi-static. It is confirmed that LICs are suitable for use as energy storage devices. [ABSTRACT FROM AUTHOR]