EOS Elettronica Organica per Strumentazione Innovativa di Ricerca

Outline Introduction PDIF-CN2: n-type behaviour and good properties Flexible n-type and p-type OTFTs Performances & Reliability Circuit Simulations Conclusions

Introduction Reliable Organic CMOS Circuits requires p- and n-type devices with: Comparable performances Stability of electrical characteristics Exploitation in flexible electronics: Plastic substrates (devices must keep high performances) P-type devices (developed, evaporated and solution-processed semiconductors, stability) N-type devices (development of evaporated materials, perylene-diimide based) PDIF-CN2 interesting performances: High crystalline films mobility (up to 6cm2/Vs) Transistor models: DC model (developed) AC model (under testing) Transient model (under testing)

Fabrication p-type channel PEN (100μm) Cytop P-type developed transitor (100 um channel length) First batch of transistors Al-Gate Cytop The molecule for p-type is under patent agreement!! © SAM channel SAM Source-Au Drain - Au PEN (100μm) Transistor architecture

Fabrication n-type Au S/D contact HMDS treatment before perylene-diimide evaporation to increase chemical stability No patent on this tipology! PEN flexible substrate Bottom-Contact/Top-Gate Au- S/D contacts, no SAM PDIF-CN2 evaporated (SPIN) (Tsub=100 °C) Gate dielectric: Cytop (550nm) Metal gate: Al Source-Au Al-Gate Drain - Au PDIF-CN2 channel Cytop PEN (100μm)

ToF-SIMS Time of Flight Secondary Ions Mass Spectrometry Ion gun Elements (ppm/ppb) Information obtained Detection of all elements and isotopes(1 – 12000 uma) Chemical information via molecular and cluster ions Detection Limits ppm of a monolayer for elements sub-fmol for molecules Spatial Location high lateral resolution (< 60 nm) high surface sensitivity (< 1 nm) high depth resolution (< 1 nm) Mass resolution 10.000 Bi+ Molecules (sub-fmol) Bi3+

ToF-SIMS – Spectra and Imaging PDIF-CN2 is homogeneously distributed. PDIF-CN2 molecular peak is present.

ToF-SIMS – Depth Profiling 29 nm

TFTs On Bare PEN Substrates Electrical Characteristics L=100 μm W=245 μm Long Channel High Ioff Good Linearity L=10 μm W=230 μm Short Channel High Ioff Contact Effects

Sample N03 HMDS treatment before PDIF-CN2 evaporation TFTs On HMDS-treated Substrates Electrical Characteristics Sample N03 HMDS treatment before PDIF-CN2 evaporation Higher mFE More negative Vth Lower Sub-Threshold Slope Higher Ion/off Still Good Linearity when channel length is scaled down

Gate-bias Stress on bare and HMDS-treated substrate devices Electrical Stability Gate-bias Stress on bare and HMDS-treated substrate devices Vgs-stress=+30V Bare Substrate Comments: Both TFTs on bare substrate and HMDS-treated substrate show very good stability with only small variation of the transfer characteristics HMDS-treated Substrate

P-type experimental characterization

P-type model

NOT in PMOS technology Standar NOT design It could be a PMOS active load

Dedicated NOT design EOS NOT design

Simulation In INV 1 INV 2 INV 3

OR Port with pass transistor approach W=120u L=5u W=120u L=5u W=10u L=100u W=10u L=100u W=10u L=100u W=10u L=100u W=10u L=100u W=10u L=100u

Conclusions N-type OTFT was analyzed with TOF-SIMS technic to improve processes and performances P-type OTFT was modelized and different logic port solutions was tested At the moment p-type OTFT circuits are under production at CNR-IMM (Rome)

Thank you!!!

Contact Resistance Contact resistance by TLM-method Rc: influence of contact resistance on characteristics of devices with different L Deviation from linear behavior Bare HMDS TLM method In both bare and HMDS-treated substrates, devices show contact resistance Rc of the same order (30 kW*cm) No SAM treatment of S/D contacts has been performed HMDS-treatment can improve the interface between PEN and PDIF-CN2 but it does not induce any improvement on contact characteristics

Chemical side ongoing OTFTs on Flexible Substrate: N-type OTFTs with evaporated PDIF-CN2 active layer have been fabricated on bare and HMDS-treated PEN substrates Devices show good performances and stability Effects of HMDS-treatment on PEN substrate: Improvement of morphological properties of evaporated PDIF-CN2 Devices made on treated-PEN show better performances with higher mFE and lower SS Rc keep the same order in the two cases Reliability: Both devices show good stability after prolonged bias stress with smaller variations of the curves at high Vgs Good stability is due to the top-gate structure and hydrophobic properties of fluoropolymer acting as gate dielectric, preventing by water/gas diffusion Future work: Future efforts will be devoted to minimize the contact resistance effects through proper functionalization of the S/D electrodes (use of SAM)