Interfacial capacitance effects in magnetic tunneling junctions

Abstract

We have fabricated magnetic tunneling junctions by oxidizing a wedge-shaped aluminum layer to produce junctions with ideal oxidized as well as under and over oxidized junctions on a single wafer. By investigating the capacitance spectra, we are able to study the effects due to interface charge accumulation. The electron–electron interaction among accumulated interface charges leads to a voltage drop inside the magnetic electrodes, resulting in the measured capacitance differing from the geometric capacitance. We have extracted an interfacial capacitance of 16 μF/cm2 per interface and a screening length of 0.55 Å for FeNi electrodes.

Parallel-leaky capacitance equivalent circuit model for MgO magnetic tunnel junctions

“…On the other hand, several reports in Al 2 O 3 based systems have observed a positive interfacial capacitance. 10,15,16 In this letter, we present the magnetic field dependence of capacitance in MgO MTJs as observed for all our junctions. A parallel-leaky capacitance based equivalent circuit has been proposed in order to account for a larger value of measured capacitance than that of the geometric capacitance.…”

“…13,14 However, the physical origin of negative interfacial capacitance is not clear and several reports in Al 2 O 3 based MTJs and MIM structures have consistently demonstrated a positive interfacial capacitance value. 10,15,16 There have been several reports of negative capacitance in Schottky barriers. [21][22][23] In these cases, however, at high bias voltage injected high energy carriers knock out charges trapped at interfaces, resulting in the depletion of interfacial charges instead of accumulation similar to impact ionization.…”

“…After theoretical predictions of spin dependent capacitances in ferromagnetic systems 8,9 , the tunneling magnetocapacitance (TMC) effect in Al 2 O 3 based MTJs has been reported. [10][11][12] However, the experimental situation for the TMC effect in MgO based MTJs is less clear with one group suggesting the existence of the TMC effect and the other group showing the absence of TMC. 13,14 The concept of negative interfacial capacitance is also controversial which has been introduced to account for the measured capacitance exceeding the geometric capacitance.…”

Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

“…By considering the parallel plate capacitor device structure of our MTJs, we calculate the geometrical-capacitance ( ) to be 10.2 nF, where A is the area of the junction (0.5 mm 2 ), d is the thickness (3-nm-thick Al yields an Al 2 O 3 tunnel barrier of 3.9 nm as [24]), and ε is the dielectric constant of Al 2 O 3 ( , = 8.85 × 10 -12 F/m).The capacitance extracted from the fit is slightly larger than the geometrical capacitance, which suggests the presence of an additional leaky capacitance in parallel to the geometrical capacitance [18], making the model unreliable for the detection of interface spin capacitance. Below we discuss a straightforward approach to detect the influence of the two interface spin-capacitances which are in principle in series with the geometrical capacitance [16,18], and give rise to the positive tunnel magnetocapacitance.…”

Electron-Electron Interaction Effects in Magnetic Tunneling Junctions

“…It is also well known that the surface layer affects the spin polarization dramatically. Recently, the electron-electron interaction effect due to bias induced charges built up at the metal-insulator interface has also been revealed [5][6][7][8]. The charge build-up at the interfaces leads to the well-known electron screening effect, causing electric field penetration into the metal [9,10], i.e.…”