Fabrication of planar-type Ni/vacuum/Ni tunnel junctions based on ferromagnetic nanogaps using field-emission-induced electromigration

Abstract

Planar-type Ni/vacuum/Ni tunnel junctions based on ferromagnetic nanogaps were fabricated by field-emission-induced electromigration in an approach that we call “activation.” In the activation method, we were simply and easily able to control the tunnel resistance of the nanogaps from 1.6 MΩ to 169 kΩ by adjusting only the magnitude of the field emission current. The resistance of the junction formed by the activation was varied by applying external magnetic fields, and the magnetoresistance (MR) ratio was approximately 12.2% at 16 K with a bias voltage of 0.72 mV. Furthermore, after the bias voltage was increased from 0.72 to 7.3 mV, the MR ratio decreased from 12.2% to 6.2%. When the applied bias voltage was fixed at 1.6 mV, the MR ratio was decreased from 11.6% to 1.2% by increasing the measurement temperature from 16 to 270 K. These results imply that it is possible to easily fabricate planar-type Ni/vacuum/Ni ferromagnetic tunnel junctions via activation.

Structural tuning of nanogaps using field-emission-induced electromigration with bipolar biasing

“…Recently, Araidai et al have found using first-principles calculations based on the densityfunctional theory (DFT) that surface atom under field emission (FE) evaporates with lower fields than the typical strength of field evaporation without FE. Then, FE-assisted surface atoms evaporate in the same direction as the electron flow [13], which is in good agreement with the direction of moving atoms controlled by the "activation" [11,12,[14][15][16].…”

“…In addition, one can facilely obtain the planar-type ferromagnetic nanogaps with Ni/Vacuum/Ni tunnel junctions using the activation with a voltage source [14]. Furthermore, we have also investigated the successful control of the nanogaps by directly adjusting the field emission current with a current source [15].…”

“…In the activation scheme, when the field emission current flows from drain to source electrode, Ni atoms at the tip of the source electrode are activated and then are migrated from source to drain electrode [11,12,[14][15][16]. Recently, Araidai et al have found using first-principles calculations based on the densityfunctional theory (DFT) that surface atom under field emission (FE) evaporates with lower fields than the typical strength of field evaporation without FE.…”

“…In order to fabricate nanogaps more simply with wellcontrolled tunnel resistance, we have already investigated a novel technique for the formation of nanogaps using EM method induced by a field emission current (so-called "activation"), based on the phenomenon of moving atoms induced by a Fowler-Nordheim (F-N) field emission current flowing through the nanogaps [11,12,[14][15][16]. In the activation scheme, when the field emission current flows from drain to source electrode, Ni atoms at the tip of the source electrode are activated and then are migrated from source to drain electrode [11,12,[14][15][16].…”

Conduction mechanism of single-electron transistors fabricated by field-emission-induced electromigration

“…We call this "activation" method. The activation method is based on moving the atoms induced by the Fowler-Nordheim (F-N) field emission current passing through the nanogaps between source and drain electrodes [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In the activation procedures, it is expected that the moved atoms accumulate within the gaps and play the dual role of reducing the gap width and forming SETs islands [15][16][17][18].…”