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MRAM read와 write line의 S-parameter 해석
박승영(S. Park),조순철(S. Jo) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.5
In this work, transmission characteristics of read and write signal were calculated when a MRAM (magnetic random access memory) cell is operated up to 10 ㎓. Test device having long read and write lines was modeled in 3 dimensions to perform a simulation. The simulation was divided into two parts, read and write operations, and S-parameters were computed utilizing FEM (finite element method) algorithm. Transmission coefficients, S₂₁, for read and write operations of MRAM device which was designed for a single cell test configuration were analyzed from DC to 1 ㎓ and DC to 10 ㎓, respectively. When the insulator thickness between the bit and sense lines was increased from 500 to 1500 Å, 3 ㏈ attenuation frequency was increased by 3.3 times, from 135 to 430 ㎒. The length of the bit and sense lines were 600 ㎛. In addition, access time was estimated by calculating the propagation delay utilizing S-parameters.
터널링 자기저항 소자의 접합면 정전용량에 따른 전기적 응답특성
박승영(S. Y. Park),최연봉(Y. B. Choi),조순철(S. C. Jo) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.2
In this research, the effects of capacitance to the access time were studied at the junction area of tunneling magnetoresistance when these were used as memory devices. These results were obtained by applying electric signal input and magnetic field was not used. We applied bipolar square waves of 1㎒ to the MTJ samples to obtain the results and time constant (τ) calculated by observing wave responses utilizing an oscilloscope. And time constant was compared with junction area. Each part of MTJ sample, such as electrical pad, lead and contact area, was modeled as an electrical equivalent circuit based on experimental results. For the 200 ㎛×200 ㎛ cell, junction capacitance was 90 pF. Also, measurement and simulation results were compared, which showed those similarity.
박승영(S. Y. Park),최연봉(Y. B. Choi),조순철(S. C. Jo) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.5
Electrostatic discharge characteristics were studied by connecting human body model (HBM) with tunneling magnetoresistance (TMR) device in this research. TMR samples were converted into electrical equivalent circuit with HBM and it was simulated utilizing PSPICE. Discharge characteristics were observed by changing the component values of the junction model in this equivalent circuit. The results show that resistance and capacitance of the TMR junction were determinative components that dominate the sensitivity of the electrostatic discharge(ESD). Reducing the resistance of the junction area and lead line is more profitable to increase the recording density rather than increasing the capacitance to improve the endurance for ESD events. Endurance at DC state was performed by checking breakdown and failure voltages for applied DC voltage. HBM voltage that a TMR device could endure was estimated when the DC failure voltage was regarded as the HBM failure voltage.
스핀밸브를 이용한 데이터 전송용 GMR 아이솔레이터의 모델링
박승영(S. Park),김지원(J. Kim),조순철(S. Jo) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.3
GMR isolator was modeled using a Wheatstone bridge which is profitable for transmitting rectangular wave digital data, and the output voltage characteristics in relation to the input current were investigated in time domain. GMR isolator modeling was divided into two parts, namely magnetic and electric parts. The flow chart of the modeling was drawn in which measured MR curve of the spin valves were incorporated to obtain the electrical voltage output. For magnetic modeling, 3-dimensional model of planar coil was analyzed by FEM method to obtain the magnetic field strength corresponding to the input current. For electric modeling, resistance, inductance and capacitance of the planar coil were calculated and magnetic field waveform was obtained corresponding to the coil current waveform in time domain. Finally, MR-H curves of spin valves and the magnetic field waveform at the spin valves were composited to obtain the output voltage waveform of the isolator. Even though the amplitude of the coil current waveform was increased by 100%, decreased by 90%, or delayed by 10% of the period compared with the input current, similar transmitted output voltage waveform to the input current waveform was obtained due to hysteretic characteristics of the spin valves at the transmission speed of over 400 Mbit/s.
박승영(S. Park),조순철(S. Jo) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.6
Linear GMR isolator which is profitable for transmitting analog signal was modeled and the output voltage and current in relation to the input current were investigated. GMR isolator modeling was divided into two parts, namely magnetic and electric parts. The flow chart of the modeling was drawn in which the MR curve of the spin valves were incorporated to obtain the electrical voltage output. For magnetic modeling, 3-dimensional model of planar coil was analyzed by FEM method to obtain the magnetic field strength corresponding to the input current. Coil efficiency of the planar coil having magnetic core layer was shown to have about 1.5 times larger than that of the coil without the magnetic core layer. The feedback coil current(output current) corresponding to the input coil current was calculated to be within ±0.25 ㎃ of the linear fitting function of Iout=Iin-5 ㎃. Also, the response time and output waveforms were obtained when the coil current was a rectangular waveform. The rise time and fall time was 6 μs, respectively when the slew rate of the op-amp was 0.3 V/μs.