Minoru Hashimoto

Magnetoresistive random access memory operation error by thermally activated reversal (invited)

The reliability in magnetoresistive random access memory (MRAM) write operation was investigated for both toggle and asteroid memory chips developed with 0.18μm CMOS process. Thermally activated magnetization reversal, being the dominant origin of the intrinsic write error, was studied theoretically and experimentally. For asteroid MRAM, the bit line or word line disturbing error on half selected bits was proved to have significant effect on the write operation margin, even in the ideal case free from bit-to-bit switching field distribution and the hysteresis loop shift. For toggle MRAM, on the other hand, the dominant origin of the error occurs for selected bits, although its impact is much smaller than in the case of asteroid MRAM. As was expected from the estimation based on the single domain model, more than 10mA operation margin with the error rate of <10−9, which is sufficiently small for semiconductor IC memory, was achieved for the toggle MRAM.

MRAM with improved magnetic tunnel junction material

Summary form only given. Increasing output and decreasing switching field distribution are very important for the development of magnetic tunnel junction (MTJ) materials, in order to achieve a high capacity MRAM. We introduce an amorphous MTJ material with excellent characteristics, which is evaluated through the MRAM/MTJ test element groups (TEG) with a MOS circuit.

A narrow track MR head for high density tape recording

In this work, the performance of a narrow track MR head/MP tape recording system was evaluated focusing on the MR head saturation. Readback density of 0.65 Gbits/in/sup 2/ was attained with reasonable SNR of 18.2 dB using a 5 /spl mu/m trackwidth MR head and thin layer MP tape. Saturation at low densities was suppressed by the selection of a run length limited 8/10 modulation code. This result suggests that the excellent performance of the narrow track MR head could increase areal density in tape recording, and would steer the development of particulate tape media toward reduction of magnetization thickness product and improvement of media noise characteristics.

Maximization of the output of shielded current perpendicular to the plane spin valve heads by optimum sense current and hard bias

The head efficiency of shielded current perpendicular to the plane (CPP) spin valve heads of 20 and 200 Gbpsi dimension has been computed and analyzed by an analytical approach utilizing the transmission line model (TLM), and a numerical approach using micro magnetic simulation. For the TLM, the effect of the circular current field was taken into account by incorporating the distribution of the effective permeability of the free layer. Both results showed higher head efficiency for the configuration where sense current field cancels the hard bias field at the front side (air-bearing side) of the free layer. The difference of efficiency by sense current direction was significant at higher sensor height and stronger hard bias. The effect was also observed experimentally on transfer curves from CPP spin valve heads of 20 Gbpsi dimension.

Sensor design of vertical type GMR head

We previously reported that the vertical GMR (V-GMR) head can be used for a high-density recording head. However, special design rules are required because the head has a different geometry from the conventional head. We discuss the optimum design of the V-GMR head. We report the technologies and materials required to produce the V-GMR head. Using computer simulations and wafer level experiments, we confirmed that the optimized V-GMR head can he used for more than 40 Gbit/in/sup 2/ areal density.

Effect of permanent magnet coercivity on transfer curve of shielded spin-valve head

The edge wall, i.e., magnetization distribution near the edge of a permanent magnet with finite coercivity was studied to investigate the stability of shielded spin-valve heads. The edge wall is structured so that the self-demagnetization field inside the permanent magnet does not exceed the magnets coercivity. 30 nm-thick CoCrPt with coercivity of 2000 Oe was sufficient to obtain a smooth transfer curve of the spin-valve head. However, if the coercivity of CoCrPt is reduced to 200 Oe or 100 Oe, a kink or Barkhausen jump will appear in the transfer curve.