Fabrication and characterization of micropillar-type multiferroic composite thin films by metal organic chemical vapor deposition using a ferroelectric microplate structure

Abstract

Using a a-axis-oriented epitaxial (Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (BNEuT) thin films with a microplate-like shape as a ferroelectric pillar material, micropillar-type CoFe 2 O 4 (CFO)/BNEuT(h00)/Nb:TiO 2 (101) composite multiferroic films were fabricated by metal organic chemical vapor deposition. The deposition time was varied from 90-150 min to examine its effect on the structural, ferroelectric, and ferromagnetic characteristics of the films. All the films exhibit single-phase cobalt ferrite with a cubic inverse-spinel structure. The deposited CFO films have a similar columnar structure with a comparatively good step coverage of 37%-66%. The room-temperature magnetization−magnetic field hysteresis loop of the films showed a clear ferromagnetic hysteresis loop, and coercivity decreased from 1.1 to 0.9 kOe with increasing the deposition time. The roomtemperature polarization−electric field hysteresis loop of the films showed a ferroelectric hysteresis loop, and the effect of the leakage current was the smallest for a deposition time of 120 min.

Effects of post-annealing temperature and micropillar shape on physical properties of micropillar-type multiferroic composite thin films

“…MP-type CoFe 2 O 4 (CFO)/BNEuT(h00) composite thin films were successfully fabricated by densely depositing CFO in the MP gaps. 21) However, we have not been able to observe a clear ME effect. This is thought to be due to the small size of the deposited polycrystalline CFO particles, which results in a small elastic interaction between magnetostriction and piezoelectricity at the interface between the ferroelectric and ferromagnetic domain walls.…”

Effects of substrate temperature on physical properties of microrod-type multiferroic composite thin films fabricated by metal organic chemical vapor deposition

“…26,32,33) Figure 5 shows cross-sectional FE-SEM images of composite films deposited at 450 °C−600 °C. As with MP-type MFs, 34) the CFO grew perpendicular to the side walls while maintaining a columnar structure. The film thickness on the top of the rod was larger than that on the side and bottom.…”

Fabrication and physical properties of microrod-type multiferroic composite thin films by metal organic decomposition

“…In recent years, we have carried out studies on the synthesis and characterization of micropillar-type multiferroic (MF) composite thin films such as CoFe 2 O 4 /(Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (CFO/BNEuT). 1,2) Most MF composite films consist of laminated structures of ferroelectric layers such as Pb(Zr,Ti)O 3 (PZT), BaTiO 3 or bismuth-layered structure compounds (BLSFs) deposited on a ferromagnetic layer such as cobalt ferrite (CFO). [3][4][5][6][7][8][9][10][11] The goal is to obtain a large magnetoelectric (ME) effect 9,[11][12][13][14][15][16] and to develop electric-magnetic energy conversion devices by reducing the clamping effect of the substrate to the utmost limit.…”

“…To achieve this, it is necessary to produce a template with a high aspect ratio by microfabricating the underlying thin film using reactive ion etching (RIE). [17][18][19][20][21] Based on the results of our previous studies, 1,2,22) we processed ferroelectric BNEuT thin films into microplates (MPs) and microrods (MRs), since ferroelectric materials containing dielectric metal elements (Bi, Nd, Eu, and Ti) exhibit high reactivity with chlorine compared with ferromagnetic materials containing transition metal elements (Co and Fe) in the RIE process. Using these underlying layers (ferroelectric pillars), we fabricated several MF composite films and examined their structural, magnetic, and electrical properties.…”

“…Based on the physical properties of the samples, the optimal deposition time was 120 min, which produced an approximately 1.1 μm thick CFO layer. 2) Using a similar MEMS technique, c-axis-oriented epitaxial BNEuT films were processed into MRs with a pitch of 2-5 μm, and a high-density CFO layer was deposited by a nonaqueous sol-gel method. In this case, it was found that the optimal pitch was 5 μm.…”