Flexible Electronics: Materials, Devices & Applications

Updated 3 September 2025

Flexible electronics are devices and circuits built on compliant substrates utilizing advanced materials like graphene and TMDCs for diverse, high-performance applications.
Innovative manufacturing techniques such as transfer-free growth and dry-transfer of 2D crystals enhance integration, scalability, and reliability.
Applications span wearables, healthcare, soft robotics, energy systems, and space platforms, driving continuous advances in device architecture and performance.

Flexible electronics (FE) technology encompasses devices, circuits, and systems fabricated on mechanically compliant substrates, leveraging low-dimensional materials, advanced device integration strategies, and application-driven architectures. FE enables conformal integration on curved, folded, or dynamically deformed surfaces, facilitating innovation in wearables, healthcare, soft robotics, rollable displays, advanced energy systems, and space platforms. Recent progress in FE critically depends on advances in materials science (notably 2D materials and organic polymers), process innovations for scalable and robust device integration, and multidisciplinary approaches to device and system modeling, design, and reliability.

1. Materials and Synthesis Strategies

A foundational pillar of flexible electronics is the selection and engineering of active and passive materials with suitable electrical, mechanical, and chemical properties. Graphene features high carrier mobility, mechanical robustness (Young’s modulus ∼1 TPa), and optical transparency (∼97% across visible-to-NIR), underpinning roles as electrodes and channels in FE (Ni et al., 2013). Beyond graphene, the family of 2D materials—transition metal dichalcogenides (TMDCs) such as MoS₂ and WSe₂, silicene, MXenes (e.g., Ti₃C₂Tₓ), and layered oxides—offers electronic, optoelectronic, and piezoresistive functionalities, often combined in heterostructures (Georgiou et al., 2012, Sahoo et al., 2022, Antonova et al., 2022).

Material synthesis routes critically determine FE performance. Two principal approaches have emerged:

Transfer-Free Growth: Direct growth of graphene on flexible substrates (e.g., polyimide, PDMS) via CVD or plasma-enhanced CVD circumvents post-growth transfer-induced defects, mitigating mechanical degradation, contamination, and mobility loss (FET electron mobilities ∼0.01 cm²/V·s, on/off >10⁴) (Pham, 2017). Metal-catalyzed or catalyst-free approaches can deliver large-area, conformal films on polymers and glass, although domain size and crystalline quality remain bottlenecks.
Dry-Transfer of 2D Crystals: Advanced dry-transfer, such as oxide-mediated transfer of monolayer MoS₂ grown on sapphire, achieves wafer-scale integration onto PET while eliminating PMMA or etchant-based contamination. The process preserves single-crystalline nature, enabling device arrays with 117 cm²/V·s mobility, subthreshold swing of 68.8 mV/dec, and on/off ratio ∼10¹² (Xu et al., 24 Jan 2025). Hybrid microprinting techniques (e.g., PPC/PVA-assisted) extend conformal electrode integration to nonplanar and flexible geometries, supporting high-mobility 2D FETs (e.g., WSe₂, MoS₂) with robust mechanical endurance (Cui et al., 25 Feb 2025).

Recent studies also introduce novel nanostructured conductors, such as FeCl₃-intercalated FLG (sheet resistance down to 20 Ω/□) for bright, gradient-free flexible lighting, and atmospheric phase-separated Pt-Ce nanonetworks (2.76 kΩ/□, stable after 1000 bending cycles at 1.5 mm radius) as ITO alternatives (Alonso et al., 2016, Baig et al., 3 Dec 2024).

2. Device Architectures and Integration Techniques

FE technology spans a wide device space, unified by requirements for flexibility and performance:

Vertical/Field-Effect Architectures: Vertical FETs employing graphene–WS₂ stacks exploit the tunability of Fermi-level–barrier alignment. Modulating the graphene Fermi energy via gate voltage (ΔE_F ≈ αV_g√n), the device switches between tunneling and thermionic regimes, achieving ON/OFF ratios >10⁶ at room temperature when transferred to PET substrates (Georgiou et al., 2012). High-mobility TMDC FETs fabricated by dry-transfer or microprinting techniques further extend to arrayed logic and sensor circuits (Xu et al., 24 Jan 2025, Cui et al., 25 Feb 2025).
Hybrid Electronic Systems: Supersonic cluster beam implantation/deposition (SCBI/SCBD) allows gold metallization of PDMS and paper-based substrates, yielding stretchable keyboards with 3D interconnects and robust via-integrated architectures for wearables and soft HMI (Bellacicca et al., 2017). Fully 3D-printed mmWave Doppler radars, employing multilayer conductive/insulating stacks and high-temperature polymers, demonstrate the extension of FE to high-frequency hybrid electronic systems (operational at 24 GHz, realized gain 12.8 dBi) (Tang et al., 2023).
Bistable Deployable Structures: FE is integrated into ultrathin bistable composite booms for space applications, where polyimide or CFRP tapes (156 μm) host flexible sensors and wiring, supporting power/data delivery and real-time dynamic monitoring in CubeSat payloads (Yao et al., 16 Aug 2024).
Flexible Energy Storage: Printable AgO–Zn batteries (SEBS substrate, PVA-KOH hydrogel, up to 54 mAh/cm² capacity) sustain high current output and mechanical bending, enabling flexible power sources matched to dynamic electronic systems (Yin et al., 2020).
Superconducting Oxide Films: Freestanding YBa₂Cu₃O₇₋ₓ films (lifted from LAO using SAO etching, transferred to PDMS, T_c ∼89.1 K) maintain superconductivity under inward and outward bending, broaden FE applicability to quantum devices and flexible sensors (Jia et al., 2023).

3. Performance Metrics and Device Modeling

Key metrics for FE span mechanical, electrical, and functional domains:

Material/Device	Mobility [cm²/V·s]	On/Off Ratio	Sheet Resistance	Mechanical/Bending Performance
TMDC FET, dry-transfer	∼117 (MoS₂)	10¹²	–	Flexible PET, high reproducibility
WSe₂ FET, microprinted	334	10⁷	5.03 kΩ·μm (Rc)	<3% μ deviation, >4000 cycles
GFET, RF operation	–	–	–	f_T 10.7 GHz, strain 1.75%
FeCl₃-FLG electrode	–	–	20 Ω/□	>1000 cycles, r ≥ 7 mm
Pt nanonetwork	–	–	2.76 kΩ/□	1000 cycles, d = 1.5 mm

Device operation is often described analytically:

For tunneling-based FE devices, current is modeled as:

$I(V) = \int \mathrm{DoS_{GrB}}(E) \mathrm{DoS_{GrT}}(E - eV) [f(E - eV) - f(E)] T(E) dE$

with transmission probability $T(E) \sim \exp[-2 (2m^*(A-E))^{1/2} d/\hbar]$ (Georgiou et al., 2012).

Mobility extraction in FETs follows:

$\mu = \frac{L}{W C_{ox} V_{ds}} \frac{dI_{ds}}{dV_{gs}}$

Performance and mechanical tolerance are assessed under repeat deformation and within metrics such as subthreshold swing, on/off ratio, and relevant endurance cycles.

4. Functional Applications and System Integration

Flexible electronics are realized across multiple technological axes:

Sensing and Wearable Applications: Flexible tactile sensor arrays employing TMDC FETs and piezoresistive composites on robotic grippers enable high-fidelity pressure mapping for real-time object classification (Xu et al., 24 Jan 2025). Graphene-ferroelectric composites (P(VDF-TrFE)-doped) yield transparent conductors (sheet resistance ∼120 Ω/□, transmittance >95%) for displays, touch panels, and optoelectronic platforms (Ni et al., 2013).
Power Electronics and Energy Systems: Printed rechargeable AgO–Zn batteries, optimized for mechanical compliance and rapid high-current discharge, power flexible E-ink display systems outperforming commercial coin cells under pulsed operation (Yin et al., 2020).
RF/High-Frequency Circuits: GFETs on flexible PEN substrates demonstrate unity-current-gain and unity-power-gain frequencies up to 10.7 GHz and 3.7 GHz, respectively, at 1.75% strain, enabling high-speed communication modules for smart tags and wearable devices (Petrone et al., 2013).
Computation with Printed and Flexible Architectures: Analog building blocks (inverter, adder, multiplier) are cascaded to realize function approximators such as Kolmogorov–Arnold Networks (KANs) for in situ signal processing. Such analog approaches yield significant area (×125) and power (10.59%) savings relative to digital implementations, with errors ∼7.58%, opening efficient on-sensor inference in size- and power-constrained FE platforms (Duarte et al., 3 Feb 2025). Machine learning circuits have been embedded (e.g., in FlexIC by Pragmatic, using sub-30 µm polyimide and IGZO TFTs, L = 0.6 µm) for ultra-low-cost healthcare and FMCG applications (Tahoori et al., 21 Apr 2025).

5. Manufacturing and Scalability

Process innovation underpins the translation of FE from laboratory demonstration to scalable deployment:

Solution/Ink-Based Processing: Conductive, semiconductive, or dielectric inks support inkjet, screen, or gravure-printed device structures. For example, devices using solution-processed PMMA:LiF composite dielectrics stainably achieve flexible FETs with gate operation voltages as low as 1 V, mobility maintained to <12% variation under large bending (Kumar et al., 2014).
Microprinting and Additive Manufacturing: Wafer-scale, direct-electrode microprinting on flexible substrates via PPC/PVA networks allows conformal transfer of electrodes to diverse geometric configurations, including surfaces as challenging as syringe tips (Cui et al., 25 Feb 2025). 3D-printers with multi-head deposition and precision via drilling enable multilayer flexible circuits (e.g., mmWave FHE radar) with robust vertical interconnects and stability under multi-axis strain (Tang et al., 2023).
Hybrid Integration and Heterogeneous Structures: SCBI/SCBD enables direct gold metallization of elastomers and paper, supporting multi-material integration for stretchable and recyclable electronics (Bellacicca et al., 2017). Layered assembly of TMDCs, graphenes, and dielectrics through van der Waals assembly or dry transfer establishes high-performance, defect-minimized interfaces (Xu et al., 24 Jan 2025).

6. Challenges, Reliability, and Future Directions

Key technical challenges span reliability under mechanical deformation, integration density, device uniformity, scalability, and sustainable material selection:

Reliability Issues: Devices endure microstructural changes under bending (e.g., crack formation in brittle materials such as ITO, trap-state formation at interfaces, aging and environmental degradation in printed ML circuits) (Baig et al., 3 Dec 2024, Tahoori et al., 21 Apr 2025). Research into cross-layer optimization—variation-aware/aging-aware design, automatic test pattern generation, and co-design of algorithms and hardware—aims to enhance system longevity.
Integration and Application Mismatch: Interface quality (e.g., polymer residues in graphene transfer, contact resistance in FETs) remains a limiting factor for mobility and switching efficiency (Cui et al., 25 Feb 2025). Next steps involve refining transfer and encapsulation processes, advancing dielectrics for ultra-low-voltage operation (e.g., down to 0.8 V in graphene/ferroelectric FTJs), and extending device architectures to support more complex, on-platform computation (Natani et al., 4 Jan 2025).
Emerging Directions: Increasing emphasis is placed on low-temperature large-area processing, sustainable and biocompatible materials, and multifunctionality (e.g., self-deploying composite booms with integrated sensing, autonomous energy solutions). Expansion into quantum devices (superconducting oxide membranes), neuromorphic computation, and multi-domain functionalities (EMI shielding, energy harvesting, and logic) is evident.

7. Summary Table: Selected Materials and Approaches for FE

Approach/Material	Key Properties/Capability	Typical Device/Application	Reference
Graphene/WS₂ FET	>10⁶ ON/OFF, transparent, flexible	Logic, transparent flexible FET	(Georgiou et al., 2012)
MoS₂ (oxide dry-transfer)	117 cm²/V·s, SS = 68.8 mV/dec, 10¹² ON/OFF	Inverters, tactile sensors, logic arrays	(Xu et al., 24 Jan 2025)
WSe₂ FET (microprinted)	334 cm²/V·s, Rc = 5.03 kΩ·μm	Flexible 2D transistors	(Cui et al., 25 Feb 2025)
Printed AgO–Zn Battery	54 mAh/cm², flexible, low Z	E-ink display powering, wearables	(Yin et al., 2020)
FeCl₃–FLG Electrodes	20 Ω/□, uniform brightness, robust	Lighting panels, foldable displays	(Alonso et al., 2016)
Pt nanonetworks	2.76 kΩ/□, 1000 cycles bend stability	Interconnects, wearable sensors	(Baig et al., 3 Dec 2024)
Silicon/IGZO FlexIC	Sub-30 μm thickness, 0.6 μm channel	Wearable ML and analog processing	(Tahoori et al., 21 Apr 2025)

Flexible electronics represents a confluence of advances in materials, processing, scalable manufacturing, and system integration, characterized by the ability to deliver robust, high-performance function on conformal, deformable substrates. Ongoing work addresses the challenges of performance scaling, reliability, and sustainable, application-driven platform engineering, with a trajectory toward broad adoption across edge, healthcare, space, consumer, and industrial domains.