Thilini Ekanayaka1,Yuchen Hu2,Esha Mishra1,Jared Paul Phillips3,Saeed Yazdani3,Alpha N'Diaye4,Jian Zhang5,Ruihua Cheng3,Peter Dowben1
University of Nebraska Lincoln1,University of Nebraska–Lincoln2,Indiana University-Purdue University Indianapolis3,Lawrence Berkeley National Laboratory4,Lawrence Berkeley National LaboratoryMolecular Foundry5
Thilini Ekanayaka1,Yuchen Hu2,Esha Mishra1,Jared Paul Phillips3,Saeed Yazdani3,Alpha N'Diaye4,Jian Zhang5,Ruihua Cheng3,Peter Dowben1
University of Nebraska Lincoln1,University of Nebraska–Lincoln2,Indiana University-Purdue University Indianapolis3,Lawrence Berkeley National Laboratory4,Lawrence Berkeley National LaboratoryMolecular Foundry5
With the increasing interest in organic molecular multiferroic electronic devices, for flexible non-volatile memory, manipulation of conductivity of various spin crossover (SCO) molecular materials has been gaining attention. Spin crossover (SCO) molecular materials are promising bi-stable magnetic materials and have been identified as an attractive candidate for memory devices. SCO molecules are transition metal based complexes which exhibit reversible spin transition between low spin (LS) and high spin (HS) states and can be fabricated into a voltage controlled device. The voltage control spin state switching of these SCO molecular thin film materials has been studied and the spin state switching by voltage leads to nonvolatile conductance change, when combined with an organic ferroelectric layer. But to make a competitive non-volatile memory device out of SCO and an organic ferroelectric, that can compete with silicon technology, there are several key criteria that need to be addressed. Building an SCO memory device with a low on-state resistance has proved to be a major challenge. The spin transition behavior of [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)] spin crossover molecule has been well studied and has been used as a successful compoent of a non-volatile memory device, although the on-state resistance is high (approximately 10<sup>3</sup> Ohm.cm). With a molecular ferroelectric gate dielectric layer, molecular SCO [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)] exhibited an on/off ratio of 4 to 5 and both isothermal switching and nonvolatility was demonstrated in the transistor device geometry. As an approach to increasing the conductivity, so as to increase the on/off ratio of the SCO molecular devices and make smaller devices practical, we have mixed TCNQ (7,7,8,8-tetracyanoquinodimethane) anions with the molecular SCO [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)]. When compared to the pure [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)] molecular thin film SCO system, the conductivity is enhanced by mixing [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)] with TCNQ. The spin transition of [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)] is also perturbed by adding TCNQ. The transistor measurements taken for the [Fe{H<sub>2</sub>B(pz)<sub>2</sub>}<sub>2</sub>(bipy)] SCO + TCNQ, with and without a ferroelectric layer, shows large charge trapping the latter case.The system shows a low charge carrier mobility and higher drift carrier lifetime which is consistent with extensive charge trapping.