Interface studies of well-controlled polymer bilayers and field-effect transistors prepared by a mixed-solvent method

Area of Science:

• Materials Science
• Organic Electronics
• Semiconductor Physics

Background:

• Semiconductor/dielectric interface properties are critical for polymer field-effect transistor (PFET) performance.
• Solvent-induced interface damage during spin-coating hinders high-performance PFET fabrication.

Purpose of the Study:

• To develop a mixed-solvent method to mitigate solvent corrosion issues in polymer bilayer deposition.
• To investigate the impact of solvent miscibility on semiconductor/dielectric interface quality and trap density.
• To optimize the fabrication of high-performance poly(3-hexylthiophene)/poly(methylmethacrylate) (P3HT/PMMA) bilayers for PFETs.

Main Methods:

• A mixed-solvent system combining an orthogonal solvent for the underlying polymer and a good solvent for the top polymer was employed.
• The ratio of orthogonal to good solvent was varied to control interface and film quality.
• Poly(3-hexylthiophene) (P3HT) was spin-coated on poly(methylmethacrylate) (PMMA) using a cyclohexane/chloroform mixture.
• Morphology characterization and electrical property measurements (including capacitance-voltage and subthreshold swing) were performed.

Main Results:

• The optimal ratio of cyclohexane to chloroform for high-quality P3HT/PMMA bilayers was determined to be 7:3.
• Transistors fabricated with the optimized bilayers exhibited good performance.
• Interface trap density was evaluated to be 3.6 × 10¹² cm^-2 eV^-1 from subthreshold swing analysis.
• Capacitance-voltage measurements indicated acceptor-type interface traps with a density of 2.3 × 10¹¹ cm^-2.

Conclusions:

• The mixed-solvent method effectively controls polymer bilayer quality and minimizes interface damage.
• Optimized P3HT/PMMA interfaces lead to improved PFET performance.
• The study provides a reliable method for characterizing and quantifying interface traps in organic semiconductor devices.