Because of their full compatibility with the modern Si-based technology, the HfO-based ferroelectric films have recently emerged as viable candidates for application in nonvolatile memory devices. However, despite significant efforts, the mechanism of the polarization switching in this material is still under debate. In this work, we elucidate the microscopic nature of the polarization switching process in functional HfZrO-based ferroelectric capacitors during its operation. In particular, the static domain structure and its switching dynamics following the application of the external electric field have been monitored with the advanced piezoresponse force microscopy (PFM) technique providing a nm resolution. Separate domains with strong built-in electric field have been found. Piezoresponse mapping of pristine HfZrO films revealed the mixture of polar phase grains and regions with low piezoresponse as well as the continuum of polarization orientations in the grains of polar orthorhombic phase. PFM data combined with the structural analysis of pristine versus trained film by plan-view transmission electron microscopy both speak in support of a monoclinic-to-orthorhombic phase transition in ferroelectric HfZrO layer during the wake-up process under an electrical stress.

The mechanism of the remnant polarization (P r) growth during the first stage of ferroelectric HfO2-based memory cell operation (the wake-up effect) is still unclear. In this work, we reveal the microscopic nature of the P r growth in functional ferroelectric capacitors based on a polycrystalline 10 nm thick (111) out-of-plane textured Hf0.5Zr0.5O2 film during electric cycling. We observe the cycle-by-cycle evolution of the domain structure with the piezoresponse force microscopy (PFM). During the early stage of the wake-up, three types of domains are found: (i) normal domains (polarization aligned along the applied electric field), (ii) nonswitchable domains with upward and downward polarization, and (iii) domains with anomalous polarization switching (polarization aligned against the applied electric field) that are commonly surrounded by nonswitchable domains. Initially, nonswitchable and “anomalous” domains are 200–300 nm in width, and they occupy ∼70% of the capacitor area. During electric field cycling, these domains reduce in area, which is accompanied by the P r growth. We attribute the domain pinning and the anomalous polarization reversal to the internal bias field of the oxygen vacancies. The local density of the oxygen vacancies decreases during electric cycling, thus producing the reduction of the internal bias field. The correlation of the PFM data with both the results of the structural analysis of fresh and cycled Hf0.5Zr0.5O2 film by transmission electron microscopy and the performance of the ferroelectric capacitor indicates that after the first cycle of the wake-up the P r growth is not associated with phase transformations, but only with the transformation of the domain structure. The obtained results elucidate the physical mechanism of the emergence of P r during the wake-up of the ferroelectric HfO2-based memory cell.

Crossbar resistive switching devices down to 40 × 40 nm2 in size comprising 3-nm-thick HfO2 layers are forming-free and exhibit up to 105 switching cycles. Four-nanometer-thick devices display the ability of gradual switching in both directions, thus emulating long-term potentiation/depression properties akin to biological synapses. Both forming-free and gradual switching properties are modeled in terms of oxygen vacancy generation in an ultrathin HfO2 layer. By applying the voltage pulses to the opposite electrodes of nanodevices with the shape emulating spikes in biological neurons, spike-timing-dependent plasticity functionality is demonstrated. Thus, the fabricated memristors in crossbar geometry are promising candidates for hardware implementation of hybrid CMOS-neuron/memristor-synapse neural networks.

The Cottage Grove formation is an active U.S. mid-continent play where cemented horizontal wells are traditionally stimulated by fracturing several perforation clusters simultaneously using limited entry "perf and plug" or other multi-stage completion solutions. Leaving sections of the lateral unstimulated when fracturing over a large interval can be even more severe in un-cemented completions, where the limited entry technique cannot be relied on to distribute the flow of stimulation fluids in the reservoir. Prior to the introduction of the sequenced fracturing technique, there was no solution to reliably stimulate a large un-cemented or openhole sections. This lead to potential losses of EUR in those wells where for some unplanned event, a section of the wellbore cannot be cemented or isolated with plugs. Recently, a well was drilled and unforeseen issues resulted in 3,300 feet of casing with a completely un-cemented annulus. A remedial cement job was not a feasible option and was quickly dismissed. It was decided to use a new sequenced fracturing technique to complete the stimulation without compromising EUR. This technique uses degradable fibers and multi-sized particles as a composite pill to temporarily plug the fractures and divert stimulation slurry to other regions along the wellbore. In this instance, 20 fracturing stages separated by 12 composite pills and 9 bridge plugs were pumped in sequence to optimize the number of fractures along the wellbore and maximize production.A production and radioactive tracer log run after the operation revealed that the composite pill successfully diverted the treatment fluids from areas previously fractured to previously unstimulated portions of the lateral. As a result, the entire lateral which had been left without cement was ultimately evenly stimulated. This was confirmed by a production log which showed a constant increase in oil and gas production compared to reference wells. Two hundred and six days after the well has been put on production, the well productivity has been more than 30% higher than any offset well.The design, execution and job evaluation of the treatments are detailed in this paper, and highlight the keys to the successful treatment which turned a well initially thought to be a failure into a technical and economic success.

No abstract