Magneto-transport properties of magnetic tunnelling transistors at low and room temperatures

Abstract

Si(100)/CoFe/AlO(x)/CoFe/FeMn/Cu/Ta magnetic tunnelling transistors (MTTs) with differing base thicknesses (W) were investigated. The magneto-transport properties of the MTTs were measured at 77 K and room temperature (RT). We obtained magneto-current ratios of 48.3% and 55.9% for emitter-base bias voltages of 1.45 and 2.0 V, respectively, at 77 K. The transfer ratios are 2.83 x 10(-5) and 1.52 x 10(-4), respectively, corresponding to bias voltages of 1.45 and 2.0 V. Moreover, the highest tunnel magneto-resistance (TMR) ratios turned out to be 12% and 20% for a base thickness of 30 A at RT and 77 K, respectively. These properties raise not only some fundamental questions regarding the phenomenon of spin-independent tunnelling at low and room temperatures, but also show some promising aspect for magneto-electronic applications. In addition, we attempted to elucidate the reason behind the outstanding TMR effect at low and room temperatures. Finally, the origin of the decrease in the mean free path asymmetry ([Formula: see text]) was clarified by using x-ray photoelectron spectroscopy profile analysis of the elements existing in the interface between Si and the CoFe base (Co, Fe, Al, Si, O).

Tailoring sidewall profiles of magnetic tunnel junctions fabricated with various etching conditions

“…In this work, we attempt to understand how well MgO-MTJs were completed where structural and compositional characteristics of the MTJ layers are investigated. Herein, MTJ stacks were fabricated as, Ta(5)/Ru(20)/Ta(5)/Mn 74 Ir 26 (15)/Co 82 Fe 18 (3)/Ru(0.8)/Co 74 Fe 16 B 10 (4)/MgO(3)/ Co 74 Fe 16 B 10 (3)/Ru(5)/Ta(5)/TiWN (50), that were grown on a Si/SiO 2 /Al 2 O 3 buffer using the ion-beam deposition technique at INESC MN, Lisbon, Portugal. 25,40,41) The layers of those stacks were all deposited at room temperature with a base pressure of ∼5 × 10 −8 Torr and finalized them with different etching conditions.…”

“…[1][2][3][4][5][6][7][8][9] Therein, a tunnel magnetoresistance (TMR) effect depends greatly on the thickness, topological properties of the free, pinned, barrier MTJ layers and/or the mean free path (MFP) of the electrons injected through those layers of an MTJ device. [10][11][12][13][14][15] In principle, majority carrier electrons with a long MFP can travel through a MTJ stack with low resistance (R ↑↑ ) when an external magnetic field aligns parallel to both magnetizations of the two ferromagnetic (FM) layers, whereas a higher resistance (R ↑↓ ) is observed if those FM magnetizations are opposite. 1,[3][4][5][6] Theoretical results showed that TMR ≈ 1100%, typically defined as (R ↑↓ −R ↑↑ )/R ↑↑ ), for a fully epitaxial MgO-MTJ could be achieved.…”

“…TMR ratio largely reduces at high annealing temperatures, effects of diffusion, migration and texture, are simultaneously included. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Despite the extensive research effort in MgO-MTJ structures, a better understanding on each MTJ and its fabrication processes at the microscopic level is indispensable. Therein, the transport properties of MTJs are largely dictated by their underlying microstructures, i.e.…”

“…Those parameters were studied by other researchers aiming at increasing TMR ratio. [3][4][5][8][9][10][11][12][13][14][15][16][17][18][19][20] Such works were taken in differing fabrication protocols in both theoretical and experimental works, i.e. tunnel spin polarized, 8,10,37) quality of barrier, crystal texture of FM layers.…”