C. S. Comstock

New low current memory modes with giant magneto-resistance materials

Memory cells made with giant magnetoresistance (GMR) material have substantial differences in resistance for the two storage states even without the presence of sense current. Because of the large outputs, static memory cells requiring reduced currents can be made. Additional memory modes can be achieved because the resistance change depends on the angle between the magnetization in the two layers rather than the angle between the sense current and the magnetization. >

Magnetization in minimum geometry M-R heads with multilayer films

A one dimensional model has been developed for the distribution of magnetization in M-R elements; the model considers elements made from double layer films and those driven by a current through the elements. The model demonstrates that both demagnetizing and exchange effects must be taken into account as the elements are reduced to micron widths. The model also provides a convenient means for calculating average demagnetizing effects and magneto-resistive response.

Dynamic switching process of sandwich-structured MR elements

The dynamic behavior of sandwich-structured magnetoresistive (MR) memory elements is studied analytically by solving Gilberts equation together with the one-dimensional micromagnetic torque equation. The typical element is 2 mu m*20 mu m and consists of two 150-AA thick magnetic layers separated by a 50-AA thick nonmagnetic layer. The easy axis is along the short dimension of the element. The theoretical study shows that wall nucleation is present when the switching is driven by a field applied in the easy-axis direction, whereas switching by a field in the hard-axis direction is accomplished by coherent rotation. The switching speed predicted by this one-dimensional model is in the nanosecond range and increases linearly with the external fields. >

2-dimensional numerical analysis of laminated thin film elements

A theoretical analysis of the laminated thin film elements is carried out by solving the micromagnetic equation. The boundary conditions of the equation are obtained by assuming that the magnetization is pinned at the edges of the elements. The dimension of the element is 2 mu m*20 mu m, with 150-AA-thick magnetic layers and a 50-AA-thick nonmagnetic layer. For the numerical analysis each magnetic layer is divided into 40*100 segments. The demagnetizing field is obtained by integrating the surface poles generated at the boundaries of the elements. Two different element shapes are considered: rectangular and diamond. Each shape is solved with its anisotropy constant either parallel or perpendicular to the long dimension of the element. >

10-35 Nanosecond magneto-resistive memories

It is known that M-R (magneto-resistive) memory elements possess the basic features necessary for a non-volatile, random access, read-write memory. Previous publications cited that an element size of 1.5 x 5 μm2 would need a read time of 3-5 μS because of the small signal level. These access times can be greatly reduced by increasing the element size in order to increase the signal level, and using a bridge formation in the read circuitry.

High speed (10-20 ns) non-volatile MRAM with folded storage elements

In magnetoresistive random access memories (MRAMs), the read access time is a function of cell size (aspect ratio). Thus it is possible to design MRAMs for a wide range of access times. A prototype MRAM chip has been designed using 250 Omega folded memory cells, two-turn word lines, and a high-speed differential sensing scheme. Simulation results indicate the total delay through the analog circuitry to be limited to 9.8 ns, thus demonstrating the MRAM access time to be within the range 10-20 ns. Even though the power consumption of the drive circuitry tends to be high when active, the nonvolatile nature of MRAMs makes them ideal for low-power applications. >

A 512 K-bit magneto resistive memory with switched capacitor self-referencing sensing

A 512 K-bit nonvolatile magnetoresistive memory with a switched-capacitor self-referencing sensing scheme is reported. This memory is economical since it requires only one mask beyond a typical CMOS process and has rad hard, scalable, and no wear-out properties. This memory has a cell size of 2.0 mu m*10 mu m, logic buried under its cells, and a 0.3 cm/sup 2/ die. It is useful for disk caches and for replacing plated wire memories in aerospace applications. >

Bias susceptibility measurements in thin permalloy films

Susceptibility measurements at 5000 Hz have been performed in the easy and hard directions on two 80-20 Permalloy films (1000 A, 1 cm in diameter) cut from large samples. The experimental results agree with the predictions of the Hoffmann theory. The susceptibility parallel to the average direction of M is found to be proportional to 1/(H - H_{k})^{7/4} or 1/(H_{k} - H)^{7/4} when the net field is large enough to prevent blocking.

Analysis of M-R elements for 10/sup 8/ bit/cm/sup 2/ arrays

Magnetoresistive memory elements made from 100-AA thick, 65% Ni, 15% Fe, 20% Co layers separated by a 40-AA nonmagnetic layer have been analyzed theoretically. The analysis shows that with lithography capable of a minimum feature size of 0.4 mu m and with the ability to deposit nonconducting magnetic keepers, memory arrays with a density of 10/sup 8/ bit/cm/sup 2/ can be achieved. Analysis shows that such elements can lead to random access memories with an access time of 5 mu s. In the case of plated conducting keepers, the element density is slightly diminished. >

Thermal noise limitations to 2×20‐μm2 magnetoresistive memory element thresholds

The effect of thermal agitation on the abruptness of the switching threshold for transverse magnetoresistive memory elements was examined. When the switching fields were within 1% or 2% of the threshold, thermal effects were observed.