Toshihiro Ishizuka

Analysis of thermal magnetic noise in spin-valve GMR heads by using micromagnetic simulation

The size of the sensor in spin-valve GMR heads has been reduced to increase the areal magnetic recording density. Thermal magnetic noise, which arises from thermal fluctuation, becomes the main source of head noise and a limitation on recording density. Insufficient abutted permanent magnetic biasing yields an asymmetrical waveform both for signal output and thermal magnetic noise. This is due to the same mechanism as that of Barkhausen noise. In contrast, it has been found that small Hex, which is the exchange coupling strength between the bottom pinned layer (Pin1) and the antiferromagnetic biasing layer, emphasizes thermal magnetic noise without affecting signal output. In a head with small Hex, the magnetization near the air bearing surface and the top of the Pin2 layer tilts in the direction of the track width and randomly flips in the opposite direction. In synthetic ferrimagnetic heads, thermal magnetic noise chiefly depends on Hex rather than unidirectional anisotropy, Hua. The value of Hua does n...

Quantitative Voltage Measurement By A Software Closed Loop Technique In Electron Beam Testing

A software closed loop technique was devised for quantitative voltage measurement in electron beam testing for LSIs. A retarding voltage of an energy analyzer is controlled iteratively by a computer to reduce difference between a slice level and a secondary electron signal to zero. The voltage is determined by the retarding voltage at the cross point of the slice level and the energy distribution curve. Using this technique, the waveform of 256 sampling phases with more than 5 V amplitude can be measured in about 30 s with 200 mV voltage resolution and 100 ps time resolution.

Electron Beam (EB) delay tester

Abstract We have developed an EB delay tester for high-speed, high-accuracy measurement of the delay time between I/O pins of LSIs. In order to replace the measured LSI in the air, the LSI is placed on a multilayer board and measurement terminals on the back of the board are put in vacuum. For high-speed and high-accuracy measurement, we made an EB column with a large EB current of 100 nA and designed measuring technique based on binary search and feedback. The parameters of all measurement terminals are registered in advance to compensate position-dependence of the s-curve. Because these parameters are affected by EB current and vary over time, they are calibrated just before the edge timing measurement. Its measuring time is 168 ms and measurement accuracy is 56 ps when specified time resolution is 50 ps and repetition rate is 2.5 MHz.

Current stability of single‐crystal and sintered LaB6 cathodes

The specimen current stability of single‐crystal and of sintered LaB6 cathodes are compared from the viewpoint of their dependence on the cathode tip temperature and the vacuum pressure. The specimen current of the single‐crystal LaB6 cathode is very stable during degradation of the vacuum in the gun chamber, while in the sintered LaB6 cathode it becomes very unstable in poor vacuum even though the total emission current is stable. The cause of this remarkable difference between the single‐crystal and sintered LaB6 cathodes is discussed.

New Logic State Measurement Technique For The Electron Beam Tester

A multi-stroboscopic sampling (MSS) technique was devised for logic state measurement with the electron beam tester. Electron beam pulses are shot and secondary electron signals are sampled m times each repetition period of LSI operation. In addition, an interpolated s-curve (IPS) method was introduced in the MSS technique for quantitative voltage measurement. Using this technique, the measurement time required for 1024 logic states was reduced by 1/70 compared to the stroboscopic waveform measurement technique.