1. Planarization of flexible ceramic substrates
Yttria-stabilized zirconia (YSZ) substrates
Substrate characteristics
- Flexible YSZ substrate (ENrG, USA)
- RMS roughness: 27.2 nm
- typical peak-to-valley distance: 100 nm
- dimensions: 40 microns (thickness), 10 mm (width)
Flexible YSZ substrate planarization with Y2O3 layers
a. Multi-layer deposition
- 4 consecutive Y2O3 layers were deposited on YSZ substrate, each undergoing an individual heat treatment
- the RMS roughness decreases from 27.2 nm for the bare substrate to 15.7 nm (4 layers)
- the layer roughness varies slightly after the second layer deposition
- RMS roughness evolution with layer number and AFM analyses are shown below
b. YSZ substrate functionalization and Y2O3 single film deposition
- the substrate surface was functionalized with a tetraethoxysilan (TEOS)/ethanol mixture 3:10 and subsequent ammonia addition, followed by a heat treatment (1h at 200 °C)
- a single Y2O3 layer was deposited by chemical solution deposition, from a propionate based coating solution with 20 % vol. added glycerol
- exeptionally low RMS roughness, 4.7 nm, was obtained
- AFM image and typical height profile are shown below
2. Buffer layer architecture
Textured MgO thin film growth
- Inclined Substrate Deposition (ISD) method was used for the growth of MgO oriented films;
- Electron beam evaporation conditions for MgO:
- base pressure: 2 × 10^(-7) Torr
- α = 45°
- deposition rate: 50 nm/s
- film thickness: 1 micron
- RMS roughness of the as-obtained thin film was 13.9 nm, and peak-to-valley distance was 113.3 nm
- Schematic diagram of the ISD method and AFM images of the as-obtained films are shown below
LaMnO3 buffer layer deposition
- LaMnO3 thin film was deposited using the Chemical Solution Deposition (CSD) method
- Precursor solution:
- lanthanum and manganese acetylacetonates (La(CH3COCHCOCH3)3· xH2O and Mn(CH3COCHCOCH3)3· xH2O) were mixed in the appropriate stoichiometric ratio in an excess of propionic acid
- final solution concentration was 0.8 M
- Precursor film was deposited on the MgO-ISD layer by spin coating
- Thermal treatment:
- 600 °C, heating rate, 5 °C/min in air - decomposition of the precursor gel
- 900 °C in air - crystallization
- Exceptionally low RMS roughness of 2.3 nm, with a peak-to-valley value of 40 nm
- 5 µm × 5 µm and 1 µm × 1 µm AFM images of the LMO thin film deposited on MgO buffer layer are presented below
3. YBCO thin film growth
- an original YBCO deposition method was proposed
- the YBCO thin film was grown using the Chemical Solution Deposition (CSD) technique
- the fluorine free coating solution was prepared using cost effective metal acetate precursors Y(CH3COO)3 ·4H2O, Ba(CH3COO)2, Cu(CH3COO)2 in a stoichiometric ratio Y3+: Ba2+: Cu2+ = 1:2:3
- 10% vol. of diethanolamine (DEA) was added to improve the solution viscosity and stability
- thermal treatment:
- 600 °C with a dwell time of 60 minutes, in humid O2 flow (20 l/hour) - pyrolisis.
- 835 °C at a heating rate of 20 °C/min, for 180 min in a humid N2/O2 atmosphere - crystallization
- 450 °C, 1 hour in an oxygen flow - oxygenation step
- X-ray diffraction confirms the epitaxial growth of YBCO, while transmission electron microscopy investigations show a film thickness of approx. 100 nm (both shown below)
- zero-resistance critical temperature, Tc(R=0) is 88.1 K
- to calculate the pinning energy, U0, the ρ(T) data is plotted in an Arrhenius form ln(ρ) vs. 1/T and fitted according to the thermally activated flux-flow (TAFF) expression (shown below)
- good agreement was found between the calculated U0 values and other repots found in literature, demonstrating that the proposed method is suitable for high-quality YBCO thin film growth
- transport measurements reveal a critical current density, Jc, value in self-field of 3 MA/cm^2
- maximum pinning force density, Fp,max, was 0.95 GN/m^3 , determined from transport measurements
- low irreversibility field value, Hirr = 2.2 T (determined as the field at which the normalized pinning force decrease below 0.01)
RF coil UV lithography mask design
- for the fabrication of the RF coil a UV lithography mask design was developed using the LayoutEditor software (shown below)
- the mask uses a standard multi-turn receiver coil geometry:
- 8 turns
- 150 µm width/turn
- outer diameter of the coil is 20 mm
- inner diameter is 17 mm