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The direct intensity modulation response of quantum cascade lasers can be accurately calculated from a three-level model. However, the calculations are algebraically complex. An alternative two-level model gives simpler expressions and more readily provides insight into the role of parameters influencing the modulation response. The object of this paper is to improve the two-level model and analyze the direct intensity modulation response. The modified model will simplify theoretical investigation of modulation related phenomena. [ABSTRACT FROM AUTHOR]

A one-dimensional heat conduction model is developed for a phase change random access memory device with an 8F[sup 2] memory cell structure (F=0.15 μm). The required current level for a reset operation, which corresponds to the phase switching from a crystalline (“1” state) to an amorphous phase (“0” state) of Ge[sub 2]Sb[sub 2]Te[sub 5], was investigated by calculating one-dimensional temperature profiles for the memory cell structure. It is revealed that a reset operation is not achieved at the current level (2 mA) reported for existing devices with a subquarter micron plug size when only TiN is used as a resistive heater. However, it is possible when an additional heating layer of 5 nm thickness is inserted between the TiN and Ge[sub 2]Sb[sub 2]Te[sub 5] layers, for which the electrical resistivity ρ[sub elec] is higher than 10[sup 5] μΩ cm, and the thermal conductivity κ and specific heat c are as low as those of Ge[sub 2]Sb[sub 2]Te[sub 5]. In addition, it is shown that a reset operation at a low current level of 1 mA can be realized in this memory cell when amorphous carbon (κ=0.2 W/m K and ρ[sub elec]=10[sup 6] μΩ cm) is used as an additional heating layer. It is believed that this relatively simple one-dimensional heat conduction model is a useful tool for analyzing the device operation of phase change random access memory devices and for selecting the proper conditions for an additional heating layer allowing for low-current operation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polycrystalline thin films of Bi-layered Sr[SUBm - 3] Bi[SUB4]Ti[SUBm]O[SUB3m + 3] (referred to as BTO for m = 3 and SBTi[SUBm] for m = 4,5, and 6 respectively) were fabricated on Pt-coated silicon substrates by pulsed laser deposition. Structures were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electric properties were investigated systematically. It was revealed that the remnant polarization P[SUBr] depended greatly on the parity of m. This dependence was well explained by using a rotating oxygen octahedra model along the a axis. The superior fatigue properties of SBTi[SUBm] (m = 4,5,6) over BTO films were discussed in detail. The high dielectric constants and low dissipation factors of the films were demonstrated. [ABSTRACT FROM AUTHOR]

A one dimensional heat conduction model has been developed for a PCRAM device with a 0.15mu m 8F2 memory cell structure in order to evaluate the required current level for a reset operation. It is believed that the model is a useful tool for estimating the operation chracteristics of phase change random access memory (PCRAM) devices with various plug structures.

Approximate analytical expressions for turn-on delay, rise time and fall time for pulse modulation of the drive current of quantum cascade lasers are presented. These time expressions are obtained using piece-wise analysis of rate equations. From the analytical expressions, the effects of laser parameters and off and on currents are discussed. A numerical analysis shows reasonable agreement with analytical results. It also confirms the predictions from analytical results. The pulse response is compared with that of near-infrared interband lasers. [ABSTRACT FROM PUBLISHER]