Fabrication of nanogap electrodes by field-emission-induced electromigration

Abstract

Controlling the tunnel resistance of suspended Ni nanogaps using field-emission-induced electromigration J. Vac. Sci. Technol. B 33, 02B107 (2015); 10.1116/1.4904731Fabrication of planar-type Ni/vacuum/Ni tunnel junctions based on ferromagnetic nanogaps using field-emissioninduced electromigrationThe authors report a simple and easy technique for the fabrication of nanogaps with separations of less than 10 nm. This technique is based on electromigration induced by field emission current. Here, the authors investigated the dependence of tunnel resistance on the shape of nanogap electrodes and initial gap separation. The initial nanogap electrodes having asymmetrical shape with the separation of 30-60 nm were fabricated by electron-beam lithography and lift-off process. In the nanogaps with asymmetrical shape, the tunnel resistance was controlled by the magnitude of the preset current during field-emission-induced electromigration and decreased from the order of 100 T⍀ to 100 k⍀ with increasing the preset current from 1 nA to 150 A. This tendency was quite similar to that of nanogaps with symmetrical shape. Furthermore, the tunnel resistance after the electromigration was less dependent on the initial gap separation and was completely determined by the preset current. This suggests that it is possible to control the tunnel resistance of nanogaps by field-emission-induced electromigration.

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 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].…”

Fabrication of single-electron transistors with electromigrated Ni nanogaps

“…Our research group has previously achieved the fabrication of SETs by using electromigration that was induced by field emission currents flowing through the nanogaps, referred to as "activation." [10][11][12][13][14] In addition, we found that the number of islands formed during the formation of the SETs can be controlled by the magnitude of the preset current used in the activation procedure. 13,14 Furthermore, we have reported the formation of a single-island SET.…”

“…The sequence of steps for performing activation on the nanogaps has been described in detail in our previous studies. [10][11][12][13][14] As shown in Fig. 1(b), following the activation, the characteristics of the SETs were investigated with dc measurements both at 18 K and at room temperature.…”