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dc.contributor.advisorWu, Judy Z
dc.contributor.authorAcharya, Jagaran
dc.date.accessioned2021-02-27T20:55:30Z
dc.date.available2021-02-27T20:55:30Z
dc.date.issued2019-12-31
dc.date.submitted2019
dc.identifier.otherhttp://dissertations.umi.com/ku:16923
dc.identifier.urihttp://hdl.handle.net/1808/31498
dc.description.abstractThe miniaturization of future microelectronics demands the development of high quality ultrathin (few to sub-nm) dielectric films for application in metal-insulator-metal (MIM) architectures. Among all other approaches employed for ultrathin dielectric film fabrication, atomic layer deposition (ALD) provides a unique approach for the fabrication of ultrathin TBs with several advantages including an atomic-scale control on the TB thickness, conformal coating, and low defects density. Despite extensive efforts in ALD devices, the figure-of-merit dielectric constant (r) exhibits a significant monotonic decrease with the film thickness as compared to bulk single crystal value. Primarily, the control over metal-insulator (M-I) interface, specifically in ultrathin thickness range, remains a challenge due to the formation of defective oxides and interfacial layer (IL). This work demonstrates the development of high quality Al/ALD Al2O3/Al MIM trilayers using a unique in-house integrated in situ deposition (sputtering/ALD) method. These trilayers devices were characterization to understand and control the IL formation with atomic precision. To the best of our knowledge, high r ~8.9 that is within 3% of the bulk value ~9.2 has been achieved for the first time on the ALD Al2O3 films in thickness range ~3.3-4.4 nm. This corresponds to an effective oxide thickness ~1.4-1.9 nm comparable to High-K HfO2 of 3-4 nm. The low leakage current density (J) ~10-9 A/cm2 is an order of magnitude lower than the best previously reported values. These results suggest that the optimal ultrathin high quality ALD Al2O3 provides a much lower-cost alternative for gate dielectric. Also, ALD Al2O3 seed layer (SL) approach was used to illustrate the critical importance of control over M-I interface to obtain dense hydroxylation and reduce incubation period, improving the dielectric properties of ultrathin ALD MgO films. ALD MgO with SL demonstrated r ~8.8-9.4 in thickness range ~3.8-4.9 nm comparable to bulk MgO ~9.4. In contrast, low r ~3.6-4.7 was observed for ALD MgO without Al2O3 SL in a similar thickness range. Both the scanning tunnelling spectroscopy and ab-initio molecular dynamics studies point out that SL allows the initial dense nucleation and perfect interface resulting in a high quality dielectric with tunnel barrier height (Eb)~1.5 eV compared to 0.8 eV for MgO without SL. This result provides an approach to engineering incompatible M-I interface using a SL for obtaining high quality dielectric as required for applications in MIM tunnel junctions and CMOS. In addition, tuning thickness of Al wetting layer (t_Al) in capacitors consisting of Nb (25 nm)/Fe (20 nm)/ALD Al2O3 (2.2 nm)/ t_Al/Fe (20 nm)/Nb (50 nm) shows switching between pure dielectric behavior for t_Al >1 nm and ferroelectric/dielectric (FE/DE) bilayer at t_Al≤ 1 nm. These FE/DE bilayer gate with ultrathin DE are promising for low power microelectronic devices. This helps to realize FE/DE bilayer capacitors with a total FE/DE total thickness 1 nm and ferroelectric/dielectric (FE/DE) bilayer at t_Al≤ 1 nm. These FE/DE bilayer gate with ultrathin DE are promising for low power microelectronic devices. This helps to realize FE/DE bilayer capacitors with a total FE/DE total thickness < 3-4 nm that show a dynamic switching on/off of the negative capacitance under the application of an external force. This result not only provides a viable approach for generating ultrathin FE/DE bilayer capacitors but also offers a promising solution to low-power consumption microelectronics and piezoelectric sensors applications. Pinhole-free and defect-free ultrathin dielectric tunnel barriers (TBs) is a key to obtaining high tunnelling magnetoresistance (TMR) and efficient switching in magnetic tunnel junctions (MTJs). Motivated by this, this work explores fabrication and characterization of spin-valve Fe/ALD-Al2O3/Fe MTJs with ALD Al2O3 TB thickness of 0.55 nm using in situ ALD. Remarkably, high TMR values of ~77% and ~ 90% have been obtained respectively at room temperature and at 100 K, which are comparable to the best reported on MTJs having thermal AlOx TBs with optimized device structures. In situ scanning tunnelling spectroscopy characterization of the ALD Al2O3 TBs has revealed a higher tunnel barrier height Eb of 1.33 eV, in contrast to Eb~0.3-0.6 eV for their AlOx TB counterparts, indicative of significantly lower defect concentration in the former. This first success of the MTJs with sub-nm thick ALD Al2O3 TBs demonstrates the feasibility of in situ ALD for the fabrication of pinhole-free and low-defect ultrathin TBs for practical applications and the performance could be further improved through device optimization.
dc.format.extent157 pages
dc.language.isoen
dc.publisherUniversity of Kansas
dc.rightsCopyright held by the author.
dc.subjectCondensed matter physics
dc.subjectAtomic layer deposition
dc.subjectdielectric constant
dc.subjectmagnetic tunnel junction
dc.subjectscanning tunnelling spectroscopy
dc.subjecttunnelling magnetoresistance
dc.subjectultrathin dielectric
dc.titleControlling Interface for Metal-Insulator-Metal Architectures with Ultrathin Dielectric Fabricated Using Atomic Layer Deposition and Sputtering
dc.typeDissertation
dc.contributor.cmtememberHan, Siyuan
dc.contributor.cmtememberMurray, Michael J.
dc.contributor.cmtememberChan, Wai-Lun
dc.contributor.cmtememberBerrie, Cindy L.
dc.thesis.degreeDisciplinePhysics & Astronomy
dc.thesis.degreeLevelPh.D.
dc.identifier.orcid0000-0003-1129-0974
dc.rights.accessrightsopenAccess


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