"NIMS" Full-Color LED Demo Unit Using 3-MTJs (TMR Devices)
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This video introduces a demonstration unit that uses light-emitting diodes (LEDs) shaped like the characters of "NIMS" to allow you to experience the mechanism of a magnetic tunnel junction (MTJ, TMR device) in an enjoyable way. The demo unit uses three MTJs on the left side. A magnetic field generated by magnets acts on each MTJ, causing its electrical resistance to change. Each MTJ is linked to the brightness of an LED representing "I" (red), "M" (blue), or "S" (green). The brightness of each letter's color changes according to the strength and direction of the magnetic field. The letter "N" achieves a full-color display by mixing the three primary colors of light: red, blue, and green. You can observe the color of the "N" rapidly changing as the brightness of the red, blue, and green lights changes.
In this demo unit, when the MTJ has a "parallel magnetization state," its resistance decreases and the corresponding color LED glows brightly. Conversely, when the MTJ has an "antiparallel magnetization state," its resistance increases and the LED dims. The brightness of the LED is finely adjusted using a technique called pulse width modulation. This technique involves rapidly switching the LED on and off hundreds of times per second while adjusting the ratio of this switching. This allows the complex magnetic field generated by the magnet to be expressed as a rich, full-color display. No microcontroller was used in its construction; it was built using an entirely analog circuit with operational amplifiers.
About the Technology Used
This demo unit employs an MTJ with a CoFeB/MgO/CoFeB multilayer structure, using a cobalt-iron-boron alloy (CoFeB) for the magnetic layer and magnesium oxide (MgO) for the barrier layer. The thin films for the MTJs were fabricated using this deposition system: Ultrahigh vacuum sputtering cluster (1). The resistance change ratio, known as the tunnel magnetoresistance (TMR) ratio, achieved through proprietary technology, exceeds 350%. This represents the world's highest level for this type of MTJs. This high TMR ratio enables the demo unit to operate with high sensitivity using inexpensive, simple circuitry. Approximately 2,000 MTJs are formed on a 2 cm x 2 cm substrate. The MTJs are extremely small, at about 10 μm (0.01 mm), and were fabricated using semiconductor microfabrication technology. For this demonstration unit, the substrate was cut into 5-mm squares. MTJs were then individually selected from these squares and connected to the circuit using ultra-fine aluminum wires.
