Ferroelectric OFET

In the transfer characteristic, we observe a shift of threshold voltage, which can be distinguished in two parts, (i) A shift of the transfer characteristic itself. 

Using PEEM, we have performed a spectromicroseopie eharaeterisation of organic devices under applied voltages. We show that the information gained from the PEEM intensity and from the related eleetron distribution eurve is 

MFIS SiO 50nm, PVDF 240nm OFET SiO, 50nm, PVDF 200nm 

We are able to distinguish between the charge carrier density, respectively, the density of 7i-electrons and the surface potential, on the other side. Thus the combination of p-PES mode and the imaging mode of PEEM offers a new analytical method for the characterisation of active layers in operating devices. 

As an example for depth profiling of interfaces, we present an XPS investigation of the ferroelectric copolymer P(VDF-TrFE). This material opens an opportunity for organic non-volatile memories. A prerequisite for low operation voltages is a downscaling of the film thickness, where interface phenomena between the electrode and the copolymer become important. We eompare the two interfaces P(VDF-TrFE)/Al and P(VDF-TrFE)/PEDOT PSS. 

---

Figure 21.11 Schematic of the ferroelectric OFET. We use P3HT as active layer and thermal evaporated Au electrodes for source and drain. The channel length is 40 pm, the channel width is 1 cm.

Figure 21.12 Source-drain current of a ferroelectric OFET without applied gate voltages, but after an applied gate voltage pulse of 73 V for 2 min. After application of negative voltage pulses, the channel resistance increases. After application of positive voltage pulses, the channel resistance decreases.

We compare two devices the ferroelectric OFET of Figure 21.12 and a similar OFET, without the ferroelectric P(VDF-TrFe) copolymer, for f/pg = -50 V, without gate bias. 

Figure 21.15 Comparison of ferroelectric MIS capacitors (MFIS) and ferroelectric OFET, as flatband shift and shift of threshold voltage, respectively, versus voltage amplitude (F2PVDF Upvdf) = AFiij. For example,...

An actual example of an extended application with technological potential is the organic and non-volatile memory, based on an OFET. The main advantage of a non-volatile memory is that its information is maintained during the readout procedure (non-destructive readout, NDRO). A ferroelectric polymer is introduced as a dielectric layer in the OFET. Due to the ferroelectric alignment of dipoles the threshold voltage of the transistor is affected by their dipole moments and can be used as stored information. 

Based on these results, we build up OFETs with a ferroelectric gate insulation, consisting of P(VDF-TrFE). 

The ferroelectric hysteresis of P(VDF-TrFE) is directly investigated by MIS capacitors and OFETs. By using MIS capacitors, a systematic shift of flatband voltage is observed, after applieation of different voltage scan windows. The MIS structures are built up as Al/P(VDF-TrFE)/Si02/Si sandwieh strueture. The dependence of the remanent polarisation on thickness of the eopolymer shows an elevated polarisation voltage for a copolymer film thiekness below 100 nm, obviously due to the above mentioned interface reaction between the eopolymer and aluminium. 

---