Effective Molecular Alignment of Semiconducting Polymer and Its Application to Photopatterned Stretchable Transistors

At a Glance

Metadata	Details
Publication Date	2025-03-05
Journal	Advanced Materials Technologies
Authors	Yasutaka Kuzumoto, Sung‐Gyu Kang, Hyunbum Kang, Sangah Gam, Hyungjun Kim
Institutions	Samsung (South Korea), Hallym University
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Mobility Stretchable OTFTs via Diamond-Processed Nanogrooves

Executive Summary

This research demonstrates a significant advancement in intrinsically stretchable organic thin-film transistors (int-OTFTs) by achieving high charge-carrier mobility through enhanced molecular alignment. The core findings and value proposition are summarized below:

Record Mobility: Achieved high mobility of 2.66 cm² Vs^-1 and a low off-current of 0.96 pA in photopatterned, short-channel (10 µm) stretchable OTFTs.
Diamond-Enabled Alignment: The critical enhancement mechanism relies on combining solution shearing with nanogrooved substrates created using a 0.1 µm diamond lapping film.
Surface Engineering Breakthrough: The nanogrooves significantly improved the crystalline structure of the semiconducting polymer, facilitating enhanced π-π stacking and molecular alignment.
Superior Durability: The resulting int-OTFTs maintained stable electrical properties under extreme conditions, showing only minor variations after 50% strain and 1000 cycles at 40% strain.
Process Optimization: Solvent treatment (1-bromooctane) was successfully applied to micro-cracked Au electrodes to reduce contact resistance, further boosting device performance.
Application Relevance: This fabrication technique is a major contribution toward realizing high-performance, stretchable display backplanes and advanced wearable electronics.

Technical Specifications

The following hard data points were extracted from the experimental results, focusing on peak performance metrics:

Parameter	Value	Unit	Context
Peak Mobility (Solution Sheared)	3.17 ± 0.21	cm² Vs^-1	On rigid SiO₂/n⁺-Si, parallel to grooves
Peak Mobility (Intrinsically Stretchable)	2.66	cm² Vs^-1	Photopatterned, transferred s-OSC
Off-Current (I_off)	0.96	pA	10 µm short channel length
Channel Length (L)	10	µm	W/L = 100/10 µm
Gate Insulator Capacitance	3.9	nF cm^-2	Cross-linked SEBS
S/D Electrode Stack	10/100	nm	MoO_x/Au
Nanogroove Tool Particle Size	0.1	µm	Diamond lapping film
Nanogroove Rubbing Pressure	0.1	kg cm^-2	Substrate preparation
Annealing Temperature	190	°C	Post-coating/post-shearing
Maximum Strain Tolerance (Static)	50	%	Parallel and perpendicular to channel
Cycling Stability	1000	cycles	Repeated stretching at 40% strain

Key Methodologies

The high-performance int-OTFTs were fabricated using a multi-step process combining surface modification, solution processing, and transfer techniques:

Substrate Preparation (Nanogrooves):
- Substrates (n⁺-Si/SiO₂ or glass) were rubbed along one axis using a 0.1 µm diamond lapping film.
- Rubbing pressure was maintained at approximately 0.1 kg cm^-2.
- The rubbed substrates were modified with an Octadecyltrimethoxysilane (ODTMS) Self-Assembled Monolayer (SAM).
Solution Shearing of s-OSC:
- The semiconducting polymer solution (DPP-P:SEBS, 3:7 weight ratio, 30 mg mL^-1 in chlorobenzene) was applied using a microtrench-patterned silicon blade.
- Shearing speeds were maintained in the range of 2-4 mm^-1 s^-1.
- Substrate temperature during shearing was held at 70 °C.
Device Fabrication (BG-BC Structure):
- A sacrificial dextran layer was coated onto the rigid glass.
- Highly cross-linked SEBS was applied as the stretchable substrate and gate insulator (capacitance 3.9 nF cm^-2).
- Micro-cracked Au electrodes (gate and S/D) were photopatterned.
Interface Engineering and Transfer:
- The S/D electrode surface was treated with Pentafluorobenzenethiol (PFBT).
- A solvent treatment using 1-bromooctane (1-BO) was applied to the S/D electrodes to reduce contact resistance (R_c), decreasing R_c from 5.1 MΩ to 790 kΩ.
- The solution-sheared s-OSC film was transferred onto the stretchable structure using a PDMS film, aligning the nanogrooves parallel to the channel length.
Final Processing:
- The s-OSC layer was photopatterned using a fluorinated photoresist to suppress parasitic current.
- The device was encapsulated with SEBS and released from the rigid substrate by dissolving the dextran layer in water.

6CCVD Solutions & Capabilities

The successful implementation of high-mobility stretchable OTFTs hinges on precise surface engineering, a domain where 6CCVD’s expertise in MPCVD diamond materials and processing is directly applicable.

Applicable Materials for Research Extension

The research utilized a 0.1 µm diamond lapping film to create the critical nanogrooves. 6CCVD offers superior, highly controlled diamond materials that can serve as advanced tooling or integrated substrates for replicating and extending this work:

Optical Grade Single Crystal Diamond (SCD):
- Application: Ideal for creating ultra-precise, highly uniform nanogrooved templates or stamps via etching/polishing techniques. SCD offers unmatched hardness and thermal stability, ensuring template longevity and consistency for high-volume solution shearing.
- Capability Match: 6CCVD provides SCD plates up to 500 µm thick with surface roughness (Ra) < 1 nm, far exceeding the precision achievable with standard lapping films.
Polycrystalline Diamond (PCD) Wafers:
- Application: Cost-effective, large-area tooling or substrates for molecular alignment studies. PCD wafers up to 125 mm in diameter can be engineered with specific surface textures to optimize polymer alignment over large areas.
- Capability Match: We offer PCD wafers up to 125 mm with custom surface finishes (Ra < 5 nm for inch-size wafers).
Boron-Doped Diamond (BDD) Substrates:
- Application: While not used in this specific OTFT, BDD is crucial for integrating stretchable electronics with electrochemical sensing (e.g., skin-like wearables). BDD provides a stable, conductive, and biocompatible electrode material.
- Capability Match: 6CCVD supplies BDD films with tunable doping levels for electrochemical applications.

Customization Potential for Advanced Devices

To move this research from lab-scale demonstration to commercial viability, 6CCVD provides critical customization services:

Research Requirement	6CCVD Customization Service	Technical Advantage
Nanogroove Tooling	Custom Diamond Templates/Stamps	We can fabricate SCD or PCD templates with defined groove periodicity and depth via advanced laser cutting and polishing, ensuring superior alignment control compared to mechanical rubbing.
Electrode Metalization	Custom Metal Stacks (Au, Ti, Pt, W, Cu)	The paper used MoO_x/Au. We offer internal metalization capabilities to deposit complex, multi-layer stacks (e.g., Ti/Pt/Au) directly onto customer-supplied substrates or diamond films, optimizing contact resistance (R_c) for stretchable electrodes.
Substrate Dimensions	Large-Area PCD Wafers	We provide PCD wafers up to 125 mm in diameter, enabling scale-up of the solution shearing process for display backplane manufacturing.
Precision Cutting	Laser Micromachining	We offer precise laser cutting services for patterning complex geometries or achieving short channel lengths (L = 10 µm) on rigid or flexible substrates prior to transfer.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond and its application in advanced electronics. We can assist researchers and engineers with similar stretchable organic transistor projects by providing:

Consultation on optimizing diamond surface energy and roughness for solution processing techniques (e.g., solution shearing, bar coating).
Guidance on selecting the appropriate diamond grade (SCD vs. PCD) for tooling based on required precision and throughput.
Expert analysis on integrating diamond materials (e.g., BDD electrodes or SCD heat spreaders) into flexible and stretchable systems for enhanced thermal and electrical performance.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Abstract Intrinsically stretchable organic transistors are promising solutions for realizing stretchable electronic systems, such as skin‐like wearables and next‐generation displays. Nevertheless, applying stretchable organic thin‐film transistors to high‐end display backplanes requires enhancing key electrical properties, including mobility and off‐current, beyond the amorphous Si level, particularly for short channel lengths. Herein, enhanced performances of intrinsically stretchable organic transistors with a high degree of molecular alignment in stretchable semiconductor composites, comprising a diketopyrrolopyrrole‐based polymer and polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene‐elastomer, utilizing the solution shearing process on nanogrooved surfaces is reported. The density and shapes of the nano grooves are controlled by the number of rubbings with a 0.1 µm diamond lapping film, achieving mobility values exceeding 3 cm 2 Vs −1 on SiO 2 /Si—three‐fold higher than that of the conventional spin‐coating method. This process improves the crystalline structure of semiconductor films, facilitating π-π stacking and large‐sized crystalline structures. Additionally, the solvent treatment on the surface of stretchable Au electrodes effectively reduces the contact resistance with highly oriented polymer semiconductors in intrinsically stretchable transistors, exhibiting 2.66 cm 2 Vs −1 mobility and 0.96 pA off‐current at 10 µm short channel length. The electrical properties of stretchable transistors yield only minor variations under 50% strain conditions and after 1000 cycles at 40% strain.

Tech Support

Original Source

DOI: https://doi.org/10.1002/admt.202500068