99.9% pure chemistry makes us best in class

History: Development of SmartKem’s OTFT chemistry

SmartKem’s intensive R&D resulted in the development of the highest performing Application Specific Organic Materials for Organic Electronics. Despite this early breakthrough, initial efforts to transfer the process to manufacturing were not successful due to significant differences in processing between the R&D line and flat panel display manufacturing. Since then SmartKem has invested resources into fully understanding all of the required process steps and has developed a range of matched passive interlayer materials to enable the high performance to be achieved.

The truFLEX® materials stack is a breakthrough technology comprising six individually designed material formulations covering every single layer in the device, starting from the initial OTFT base layer all the way through to the final passivation layer chemistry. The ink set includes the active organic semiconductor formulation and a series of orthogonal passive interlayer inks (Base layer, Self-Assembled Monolayer, Organic Gate Insulator, Sputter Resistant Layer and Passivation layer). SmartKem’s proprietary materials set is covered by an extensive IP portfolio comprising over 220 patents worldwide.

The truFLEX® materials set is designed to deliver high value customer benefits in mass production where process compatibility of the chemistry is a demanding prerequisite. All truFLEX® materials are entirely compatible with industry-standard production equipment.The truFLEX® materials set is designed to deliver high value customer benefits in mass production where process compatibility of the chemistry is a demanding prerequisite. All truFLEX® materials are entirely compatible with industry-standard production equipment.

What makes truFLEX® materials best in class?

The successful development of the truFLEX® materials set was due to Smartkem bringing together a team of scientists having the right skill sets and expert knowledge to design, develop and put into practice the best total technical solution in the field of organic electronics. The key skills required included organic chemistry, formulation chemistry, device physics and process engineering.
 

Organic Chemists

  • Molecule discovery
  • Design viable synthetic routes
  • Implement material purification
  • Transfer lab chemistry processes to industrial scale-up partners

Ink Formulation Scientists

  • Formulation of OSC and passive interlayer inks orthogonal to underlying layer
  • Inks compatible with range of solution coating techniques (spin coating; slot-die; ink jet…)

Device Physicists

  • Fabricate devices to test OSC and stack materials
  • Experts in device characterisation & statistics
  • SPICE model circuit simulation

Process Engineers & Prototyping Facility (CPI)

  • Transform R&D device fabrication processes into industrially relevant processes that are then transferred to customers’ lines.

SmartKem’s approach in developing the organic semiconductor formulations was to design a series of high mobility polycrystalline small molecule(s) that are combined with matched, high permittivity semiconducting oligomer(s). The benefits of this small molecule/oligomeric binder approach include:

  • Enabling solution coating of large area substrates with resulting high uniformity of the OSC layer. Incorporation of the semiconducting binder enables the end-user to process the truFLEX organic semiconductor ink as if it is a polymer.
  • High mobility devices (µ >3 cm2V-1s-1 @ L=3.5µm)

SmartKem also has extensive know-how relating to design of the matched semiconducting binders. Key binder design parameters include:

  • Design of the surface free energy of the oligomer to enable phase separation of the small molecule to the required device interface.
  • Control of the HOMO level of binder is important to ensure charge transport occurs via the high mobility small molecule.
  • Design of the permittivity of the semiconducting binder is key to controlling large area uniformity.
  • Matching binder polarity to the base layer and to the SAM to enable large area uniformity of the OSC layer.

SmartKem has worked with industry leading chemical companies (both European and US) to successfully scale-up the active semiconductors to multi-kilo batch sizes. truFLEX® formulated inks are available in 100s-1000 litre volumes compatible with mass production.

To deliver electrically stable devices, SmartKem scientists understood that all interlayers in the OTFT stack had to be free from contaminants, particularly ionic impurities.

SmartKem’s interlayer photochemistry does not generate any ionic contaminants. The interlayers are cured using proprietary free radical chemistry, delivering inks, that can be cured in air to afford thin films (< 200nm). Interlayers are IP protected.

Base Layer, Organic Sputter Protective Layer and Passivation layer inks are directly photo-patternable using existing photolith equipment (compatible with i, h, g-line and broadband).

The SmartKem approach results in OTFTs having minimal ionic impurities which in turn affords OTFTs having the best-in-class bias stress stability, lowest Ioff values (< 10-14 A), highest on/off ratios (> 109).

It is important to avoid use of cationically cured interlayers. These materials rely on photogenerated acids to effect cure which gives rise to high levels of ionic contamination. Results in highly doped OTFTs, as evidenced by high bias stress instability; high Ioff values, & low Ion/off ratios.

Components of truFLEX® Organic Semiconductor Inks

SmartKem’s approach in developing the organic semiconductor formulations was to design a series of high mobility polycrystalline small molecule(s) that are combined with matched, high permittivity semiconducting oligomer(s). The benefits of this small molecule/oligomeric binder approach include:

  • Technical team has excellent understanding of formulations
  • In-depth knowledge of how to combine small molecule/polymer/additives to maximise the performance of OSC layer and the resulting oTFT
  • More than 50 man years expertise relating to OSC formulation

High mobility, small molecule

  • Intrinsic mobility ≥ 20 cm2V-1s-1
 

Semiconducting polymer ‘controls’ :

  • Morphology of OSC layer
  • Phase segregation & uniformity of SM
  • Viscosity of ink
 

Solvents

  • Solubilise SM & Binder
  • Modify surface tension
  • Influence ink viscosity
  • Solvents for printing

truFLEX® technology advantages for printing

  • SmartKem’s OSC materials are soluble in a range of low toxicity organic solvents enabling wide ink formulation latitude and providing for control of evaporation rate of a range of droplet sizes (tens of picolitres and below).
  • SmartKem’s technical approach of combining a high mobility polycrystalline small molecule with a matched semiconducting binder enables a wide formulation latitude and a wide range of printing methods. Rheology control of the ink is achieved through design of the chemistry of the binder, molecular weight selection/control and solids loading of the binder in ink
  • The use of semiconducting binders enables control of phase separation of the high mobility small molecule, improving control of crystal morphology and enabling large area uniformity in manufacture
  • SmartKem has an extensive range of high permittivity binders having customisable electronic properties to fine tune charge injection at short channel lengths
  • Excellent uniformity is achieved through application of SmartKem know-how matching the surface energy values of the interfaces on the substrate to be printed (e.g. metal electrode; planarisation layer, semiconducting inks. SAM materials can be used for droplet positioning and carrier injection
  • truFLEX® Ink formulations are compatible with a range of printing techniques including spin, slot-die and ink jet printing
  • Organic TFTs offer the only truly flexible/foldable backplane technology
  • truFLEX® scores highly on many of the key criteria for the next generation of displays

truFLEX® manufacturing process presents further advantages beyond other backplanes:

  • lower thermal budget
  • ease of large area processing
  • fewer mask steps than a-Si or LTPS

CPI facility overview

  • UK’s premier facility for printable and plastic based electronics processing
  • 800 m2 class 100 and 700 m2 class 1000 clean rooms
  • Cassette in/out and robot handling of substrates
  • Plastic to glass lamination
  • Sputter, wet etch & dry etch systems, ALD system (S2S and R2R)
  • AOI (CD overlay), large area film thickness mapping, semi-auto e-test, defectivity identification (Orbotech)