Static information storage and retrieval – Associative memories – Magnetic cell
Reexamination Certificate
1998-12-31
2001-01-16
Phan, Trong (Department: 2818)
Static information storage and retrieval
Associative memories
Magnetic cell
C365S170000
Reexamination Certificate
active
06175515
ABSTRACT:
BACKGROUND
The present invention pertains to memory devices. Particularly, it pertains to nonvolatile memory devices, and more particularly, the invention relates to magnetic memories with Hall effect sensing.
The related art appears not to reveal the present Hall-type device, which is a micromachined solid-state, vertical standing memory cell. Other authors have not discovered the operation in the carrier saturation velocity regime, which leads to the highest signal. The device has high reliability and a good high signal memory with low-power consumption. The related art also does not appear to show a vertically structured magnetic memory on an integrated circuit having high density.
SUMMARY OF THE INVENTION
The present invention is a vertically integrated magnetic memory (VIMM) with Hall effect sensing or reading. It has a ferromagnetic structure with a nearly enclosed magnetic path, which is a vertical structure integrated on a chip. The Hall effect is the creation of an electric voltage inside a semiconductor when it is conducting an electric current in the presence of a magnetic field. This electronic field pushes the electronic carriers to one side of the semiconductor, giving rise to the Hall voltage. The Hall voltage is proportional to the applied magnetic field and the electric current. A signal or voltage of a Hall effect can be represented by equation V
H
e {dot over (V)}×{dot over (H)}. {dot over (V)} is the velocity of the electron, and e is the charge of the electron. {dot over (H)} is the magnetic field. The measurement of the Hall voltage can be used to determine the number of current carriers per unit volume within a semiconductor device and also whether the carriers are positively or negatively charged.
Each memory cell has a closed magnetic field that has high strength for a strong Hall effect. The magnet is a closed loop, robust reproducible magnet. A memory array of such cells uses little power in that only few cells need to draw the read current for a short time required to read the information. A silicon chip implementation of the memory is one embodiment wherein the field required to saturate the electrons can be achieved without excessive power. Implementation of the cell may also be in GaAs, indium gallium arsenide, indium phosphide, indium arsenide and so forth which have a lower saturation field than silicon. The GaAs implementation is described below, and is the best approach for the invention. There is a robust differential current readout. Operation of the Hall memory device is at the saturation electric field where the highest electron velocity can be attained for the best Hall effect, which can be shown on an electron velocity versus the electric field graph. Operation in the electron velocity saturation region offers a high read-out signal at low power. The concentric crossection of the device allows for a low power write.
A high density of these memory cells is achieved due to vertical structure and integration of the cells on a substrate. The size of each cell may be as small as a ten-micron square. This size permits up to 10 million cells on a one-centimeter square chip.
Features of the invention relative to comparable prior art are higher carrier velocities, stronger magnetic fields and a robust magnetic circuit design. These features provide for better and more reliable signals, and no creep from half-currents in the write mode from one of the two conductive lines that carry current to change the direction of magnetic field. If the cell is not being addressed, there may be a current in one line, which may weaken the magnetic field in a prior art device. Such half-current does not affect the present cell because of its vertical structure and the closed loop magnetic circuit. Half-select write currents cause a creep of magnetization or domains in half-selected cells, which leads to reliability problems. The closed magnetic loop prevents such creep.
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Berndt Dale F.
Detry James F.
Peczalski Andrzej
Honeywell International , Inc.
Phan Trong
Shudy, Jr. John G.
Tran M.
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