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Materials for Energy efficient ICT

We work on designing and nanoengineering oxide thin film to create improved energy efficient ICT devices.

We work on designing and nanoengineering oxide thin film to create improved energy efficient ICT devices. Some of the work is basic science (i.e. understanding interface effects in electronic oxide films) while other parts are more applied.  Below we discuss recent example results on magnetoelectrics, magnetics, and oxides for CMOS flexlogic.

a) Large Perpendicular Exchange Bias Above RT for MRAM applications

In all-oxide-based spintronic devices, large exchange bias effect with robustness against temperature fluctuation and compatibility with perpendicular magnetic recording is highly desired. In one of our recent works, rock-salt antiferromagnetic NiO with a Neel temperature (TN) of ∼525 K and spinel ferrimagnetic NiFe2O4 with a high Curie temperature (TC) ≈ 790 K and TC > TN were chosen as compatible materials to form a well-phase-separated, vertically aligned nanocomposite thin film. In this nanoengineered thin film, an exchange bias effect with a blocking temperature far above room temperature has been achieved. A large perpendicular exchange bias field of up to 0.91 kOe with an interfacial exchange energy density of 0.11−0.34 erg/cm2 was obtained at room temperature. The results demonstrate that proper choice of the phases (including use of non-perovskite compositions) and careful strain engineering and nanostructure engineering (proper substrate) makes oxide nanocomposites strong potential candidate systems for next generation spintronic devices.

 

Figure1

Figure 1 (a) Cross-sectional EDS elemental maps of the NiO-NFO film (green: Fe, red: Ni, blue: Ti), (b) X-ray diffraction ω-2θ scan, (c) the  room temperature exchange bias measured along OOP direction after field cooling with magnetic field of 1 T, and (d) the temperature dependence of the exchange bias field of a NiO-NiFe2O4 vertically aligned nanocomposite film grown on the STO (001) substrate.

Reference:

Rui Wu, Chao Yun, Xuejing Wang, Ping Lu, Weiwei Li, Yisong Lin, Eun-Mi Choi, Haiyan Wang, Judith L MacManus-Driscoll. All-Oxide Nanocomposites to Yield Large, Tunable Perpendicular Exchange Bias above Room Temperature. ACS Appl. Mater. Interfaces, 2018, 10 (49), pp 42593–42602 (DOI: 10.1021/acsami.8b14635)

b) New Science of Oxide Interfaces

Electric field control of magnetism could provide for low power, ultra-high density non-volatile memory. However, despite intensive research efforts, no practical materials systems have emerged. Interface-coupled, composite systems containing ferroelectric and ferri-/ferromagnetic elements have been the most promising, but they have many problems, e.g. substrate clamping, large unwanted currents (leakage), and they cannot be miniaturized to give high density recording. Through careful materials selection, design, and nanoengineering, we have demonstrated a high-performance room temperature magnetoelectric system. A vertically aligned nanocomposite structure in which the strain coupling is independent of the substrate was used and a new, low leakage ferroelectric material was employed. A large converse magnetoelectric coefficient was achieved of >10-9 s m-1.

figure2

Figure 2: ME effect in the VAN film. (a) AFM image of the sample surface. (b) Schematic illustration of the strain mediated ME effect VAN films. (c) Magnetic hysteresis loops along the OOP direction and (d) magnetic hysteresis loops along the IP direction with and without applying in-situ voltages.


Reference:

Rui Wu, Ahmed Kursumovic, Xingyao Gao, Chao Yun, Mary E. Vickers, Haiyan Wang, Seungho Cho, and Judith L. MacManus-Driscoll. Design of a Vertical Composite Thin Film System with Ultralow Leakage To Yield Large Converse Magnetoelectric Effect. ACS Appl. Mater. Interfaces, 2018, 10 (21), pp 18237–18245 (DOI: 10.1021/acsami.8b03837)


c) Atmospheric pressure spatial ALD (AP-SALD) for CMOS printed logic

High quality, low-temperature-grown thin film metal oxides are urgently needed for a wide range of emerging electronic applications relating to the Internet of Things. Low power consumption is key, particularly in devices for energy harvesting and for RFID. Reducing power consumption would greatly expand the technology’s market opportunities.  We are particularly interested in printed logic on flexible substrates. Owing to the low availability of simple p-type materials with sufficient carrier concentration and mobility, the focus to date has been on nMOS logic. CMOS is highly preferable, however, owing to the low power requirement. However, CMOS requires both n-type and p-type materials, but simple p-type materials with the required carrier concentrations are scare. Hence, we are developing p-type oxides grown at low temperature using AP-SALD.

 

A recent review we have written on the prospects and challenges of ALD for oxide electronics will be published in the “Roadmap of Oxide Technologies for Electronic Applications 2018” (MacManus-Driscoll JL and Napari M, Atomic Layer Deposition of Oxides:  Benefits, Challenges and Future Directions, Applied Surface Science, 2018). Some example information on our recent growth of p-type NiO films is shown in Fig. 3 below.

Figure 3. AP-SALD system schematic with precursors shown for growth of p-type NiO films, AFM image of film grown on glass with RMS roughness of 0.67 nm, and Mott Shottky plot indicating hole carrier concentration of 1018cm-3, courtesy of Lana and Mari Napari (unpublished).

Figure 3. AP-SALD system schematic with precursors shown for growth of p-type NiO films, AFM image of film grown on glass with RMS roughness of 0.67 nm, and Mott Shottky plot indicating hole carrier concentration of 1018cm-3, courtesy of Lana and Mari Napari (unpublished).

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