Research // Semiconductor Thin Films

FeCo/CoFe Thin Film Fabrication on Flexible Substrates Using DC Magnetron Sputtering

This research investigates the fabrication and characterization of Fe₆₀Co₄₀ and Co₉₀Fe₁₀ thin films deposited on flexible polyimide (PI) and PET substrates via DC Magnetron Sputtering. The study focuses on optimizing deposition parameters to achieve controlled magnetic anisotropy, saturation magnetization, and low coercivity for flexible spintronic sensor applications.

Research Objective

Optimize magnetic properties of FeCo/CoFe ferromagnetic alloy thin films on flexible polymer substrates for applications in flexible magnetoresistive sensors and spintronic devices.

Materials

Fe₆₀Co₄₀ (Iron-Cobalt)

Role: Ferromagnetic alloy target

Thickness: 50-200 nm

Co₉₀Fe₁₀ (Cobalt-Iron)

Role: Ferromagnetic alloy target

Thickness: 50-150 nm

Polyimide (PI)

Role: Flexible substrate

Thickness: 50-125 µm

PET

Role: Flexible substrate

Thickness: 100-200 µm

Deposition Parameters

  DC POWER SUPPLY ──┬── TARGET (FeCo/CoFe)
                    │
  Ar GAS (20 sccm) ──┼── PLASMA ── SUBSTRATE (PI/PET)
                    │
  VACUUM PUMP ──────┴── CHAMBER (5e-6 Torr base)

TechniqueDC Magnetron Sputtering

Base Pressure5 × 10⁻⁶ Torr

Working Pressure3 × 10⁻³ Torr (Ar)

Substrate TemperatureRoom Temperature (25°C) to 300°C

Target-Substrate Distance80 mm

Sputtering Power50-150 W DC

Deposition Rate0.5-2 Å/s

Gas Flow20 sccm Ar (99.999% purity)

Substrate Rotation10 rpm for uniformity

Fabrication Workflow

Substrate Preparation

Flexible PI/PET substrates cleaned ultrasonically in acetone, isopropanol, and deionized water (10 min each). Dried in N₂ flow. Surface treatment via O₂ plasma (50 W, 2 min) to improve adhesion.

Vacuum System Pumpdown

Chamber evacuated to base pressure 5 × 10⁻⁶ Torr using turbomolecular pump backed by rotary vane pump. Substrate heated to target temperature at 5°C/min ramp rate.

Pre-Sputtering

Target surface cleaned by 5 min pre-sputtering with shutter closed. Removes surface oxides and contaminants. Power stabilized at target level.

Thin Film Deposition

DC plasma ignited in Ar atmosphere. Deposition rate monitored via quartz crystal microbalance (QCM). Film thickness controlled by deposition time at calibrated rate.

Post-Deposition Annealing

Selected samples annealed in vacuum at 200-400°C for 1 hour to study structural relaxation and magnetic property evolution.

Characterization

Multi-technique characterization: XRD for phase identification, VSM for magnetic hysteresis, FMR for dynamic properties, FESEM/EDS for morphology and composition.

Characterization Pipeline

[XRD (Rigaku Ultima IV)]Bragg-Brentano geometry, Cu Kα radiation (λ = 1.5406 Å)

Measures: Phase identification, crystallite size (Scherrer), lattice strain, texture analysis

[VSM (LakeShore 7400)]Room temperature hysteresis loops, ±2 T field range

Measures: Saturation magnetization (Ms), coercivity (Hc), remanence (Mr), squareness ratio

[FMR (Bruker E500)]X-band (9.5 GHz), in-plane and out-of-plane angular dependence

Measures: Gilbert damping constant (α), anisotropy field (Hk), resonance linewidth (ΔH)

[FESEM/EDS (Zeiss Gemini)]In-lens SE detector, 5-15 kV accelerating voltage

Measures: Surface morphology, film thickness cross-section, elemental composition mapping

[AFM (Bruker Dimension)]Tapping mode, 10 µm × 10 µm scan area

Measures: Surface roughness (Rq, Ra), grain size distribution, 3D topography

Experimental Results

saturation Magnetization

FeCo: ~2.1 T, CoFe: ~1.8 T (measured via VSM)

coercivity

FeCo: 15-25 Oe, CoFe: 5-10 Oe (thickness dependent)

damping Constant

FeCo: α ≈ 0.008, CoFe: α ≈ 0.012 (FMR measured)

surface Roughness

Rq < 1.5 nm for films ≤100 nm thickness (AFM)

crystal Structure

BCC α-FeCo phase confirmed (XRD 2θ = 44.8°)

anisotropy

In-plane uniaxial anisotropy observed, Hk = 50-80 Oe

Target Applications

▸Flexible magnetoresistive sensors for wearable electronics
▸Magnetic field sensing in biomedical devices
▸Spintronic logic devices on polymer substrates
▸Micro-actuators and flexible MEMS systems
▸Non-contact position and rotation sensing

Future Scope

▸Investigate thickness-dependent magnetic properties in ultrathin regime (<20 nm)
▸Study exchange bias effects in FeCo/CoFe bilayer structures
▸Integrate films into flexible spin-valve device stacks
▸Characterize high-frequency performance up to 40 GHz
▸Develop transfer printing process for heterogeneous substrate integration

Methodology

DC SputteringXRDVSMFMRAFMFESEM

Material System

TargetFe₆₀Co₄₀

TargetCo₉₀Fe₁₀

SubstratePI / PET

Thickness Range50-200 nm

Characterization

Structural: XRD Phase ID

Static Magnetic: VSM

Dynamic Magnetic: FMR

Morphology: AFM/FESEM

Composition: EDS

Research conducted at Materials Science Laboratory, Department of Electronics, University of Delhi. Data obtained from experimental batches under controlled laboratory conditions.