Pinholes and temperature-dependent transport properties of MgO magnetic tunnel junctions

Abstract

Magnetic tunnel junctions ͑MTJs͒ with thin crystalline MgO͑001͒ barriers displaying large tunnel magnetoresistance ͑TMR͒ and low resistance-area product ͑RA͒ will likely be used as the next generation sensors in read heads of ultrahigh-density hard drives. However, the thin insulating barrier may result in the presence of metallic pinholes joining the two electrodes. Here we study the transport properties of thin MgO-based low resistance MTJs ͑barrier thickness t = 7.5 Å͒, deposited by magnetron sputtering, with RA values of ϳ40 ⍀m 2 , reaching TMR values of ϳ60-75% at room temperature. We performed temperature-dependent ͑300-20 K͒ resistance ͑R͒ measurements and observed different behaviors for different magnetic states: positive dR / dT for the parallel ͑P͒ state, attributed to the presence of pinholes in the barrier, but a mixed character in the antiparallel ͑AP͒ state, with dR / dT changing from negative to positive with decreasing temperature. This indicates an interesting competition between tunneling and metallic transport in the studied samples. To explain this transport behavior, we developed a simple model with the two conducting channels, tunnel and metallic, in parallel. The model assumes a linear variation of the electrical resistance with temperature for both conducting channels and its dependence on the MTJ magnetic state ͑P and AP͒. The modeled results show that the sign of dR / dT does not give an indication of the dominant conductance mechanism and that the crossover temperature at which dR / dT changes sign depends strongly on the linear electrical resistance-temperature coefficients. We performed fits to our experimental R͑T͒ data, using the proposed model, and observed that such fits reproduced the data quite well, illustrating the validity of the model.

Programmable ferroelectric tunnel memristor

“…The time scale of the writing pulses to access these intermediate states is in the sub-μs range, which is comparable with the switching time of ferroelectric polarization that has been shown in previous studies [20]. While the absolute values of the saturated (R ON and R OFF ) tunnel resistances might slightly vary, mostly due to additional conducting paths represented by defects, [21] the R ON /R OFF ratio remains constant irrespective of the write amplitude and/or width.…”

Transparent CdO/n-GaN(0001) heterojunction for optoelectronic applications

“…The series resistance dependence of non-linear current-voltage (I-V) characteristics is also associated with pinholes and voids. On the other hand, the presence of pinholes leads to a thin barrier, modeling a tunnel across the barrier [58].…”

Evidence of spin-polarized direct elastic tunneling and onset of superparamagnetism in MgO magnetic tunnel junctions

“…Judging from the form of the G͑T͒ curves, where an overall increase of G P,AP with increasing T is observed ͑for the low T anomaly of the MTJ with t fl = 1.55 nm, see below͒, we exclude the existence of metallic pinholes across the barrier. [41][42][43] Furthermore, G P increases only slightly on our MgO-based MTJs, a characteristic feature of high quality MgO tunneling barriers. [20][21][22][23] …”