Jianfei Yu

Electrical characterization of polymer-based FETs fabricated by spin-coating poly(3-alkylthiophene)s

The current-voltage (I-V) characteristics of two different polymer thin-film transistors (TFTs), based on spin-coating of poly(3-hexylthiophene)-P3HT and poly(3-hexadecylthiophene)-P3HDT, are studied. A model is developed to interpret the results and to explain the differences between these two polymers. Various parameters of the semiconducting polymers, including bulk mobility, field-effect mobility, trap density, and unintentional dopant concentration are estimated. The model takes into account the domination of the bulk current over the channel current in the subthreshold regime as well as the effects of the depletion layer as parasitic resistances in series with the channel resistance. Furthermore, the effects of the films thickness on the electrical characteristics of these TFTs are discussed. Compared to the P3HT, the P3HDT-based TFT has a lower subthreshold slope, higher on current ratio, and higher field-effect mobility.

Temperature dependence of breakdown voltages in separate absorption, grading, charge, and multiplication InP/InGaAs avalanche photodiodes

In this paper, we investigate temperature dependence of breakdown voltage V/sub br/ from -40 to 110/spl deg/C in separate absorption, grading, charge, and multiplication (SAGCM) InP/InGaAs avalanche photodiodes (APDs) with a range of device parameters. The experimental data shows that V/sub br/ is approximately a linear function of temperature, with a temperature coefficient /spl eta//sub exp/ between 0.13 and 0.16 V//spl deg/C. A physical model is developed and it demonstrates that V/sub br/ indeed varies linearly with temperature with a temperature coefficient /spl eta//sub the/ about 0.155 V//spl deg/C. It also explains successfully the small variation of /spl eta//sub exp/ among the APDs. Good agreement between the physical model predictions and experimental data of published InP-based APDs is also obtained. This good agreement demonstrates that the proposed physical model is appropriate to model the temperature dependent characteristics in any InP-based APDs. >

CHEMICALLY AMPLIFIED PHOTOLITHOGRAPHY OF A CONJUGATED POLYMER

The solid state photocatalytic reaction between trifluoromethanesulfonic acid and poly{3-[2-(tetrahydropyran-2-yloxy)ethyl]thiophene} is employed to fabricate polymeric patterns of conjugated polymer.

Variable current transport in polymer thin film transistors

The performance of polymer thin film transistors, made of different semiconducting polymers, depends mostly on the type of polymer and its deposition conditions. For these polymer field-effect transistors (PFETs), the current transport is limited by the carrier injection from the source electrode into the polymer. The disordered polymer molecules near the injection interface randomize and decrease the injection barrier, resulting in a large variation of the PFET characteristics, such as threshold voltage, leakage current, and mobility. The PFET current–voltage characteristics degrade at temperatures higher than 40 °C and the low frequency noise increases by 0.3 dB/°C.

Chemically amplified soft lithography of a low band gap polymer

A solid state, acid-catalyzed reaction leading to chemically amplified soft lithography is demonstrated with a low band gap conjugated polymer; poly({3-[11-(tetrahydropyran-2-yloxy)undecyl]thiophene-2,5-diyl} -3,4-ethylenedioxythiophene-2,5-diyl).

Instability of the Noise Level in Polymer Field‐Effect Transistors with Non‐Stationary Electrical Characteristics

The low frequency noise (LFN) properties of field-effect transistors (FETs) using polymers as the semiconducting substrate material are investigated and explained in terms of the charge carrier transport in polymer thin-film structure. Three mechanisms contribute to the carrier transport - charge injection from source electrode into polymer, charge hopping between polymer molecules for drift transport toward the drain, and charge buildup, probably at polymeroxide interface. Charge buildup is responsible for non-stationary electrical characteristics, but does not contribute significantly to the LFN. Charge hopping determines the maximum value of the mobility and the minimum value of mobility 1/f noise. The variations of the PFET characteristics are mainly due to dispersion in the injection barrier of source-to-polymer contact. High disorder in the polymer at the source contact can increase the leakage current in PFET and can introduce number fluctuation S-GN in the polymer conduction on top of the mobility fluctuation. SGN is proportional to the DC power applied to the injection barrier and should be assumed as a voltage source, since carrier hopping in the polymer reduces the effect of the injection noise. At present, the physical origin of SGN is not fully understood.

Noise and charge transport in polymer thin film structures

The low frequency noise (LFN) properties of the field-effect transistors (FETs) using polymers as the semiconducting material in thin-film transistor (TFT) structures are investigated and discussed in terms of the charge carrier transport. Results obtained from several research groups are summarized. Injection-drift limited model (IDLM) for charge transport in amorphous PFETs is discussed. IDLM has some advantages in comparison to the commonly used metal-oxide-semiconductor (MOS) transistor models. A general trend of proportionality between noise power density and the DC power applied to the polymer FET’s (PFET’s) channel is observed in the data from several research groups. This trend implies mobility fluctuation in PFET as the dominant noise source.