Graphene field effect transistors using TiO2 as the dielectric layer

ANDRES BOTELLO; CARLOS BORJA HERNÁNDEZ; LAURA N. SERKOVIC LOLI; PEDRO FLORES SILVA

Congreso; Graphene 2020; 2020

Graphene based electronic devices face thechallenge to find a suitable dielectric material which has little or negligibleeffect in diminishing graphene?s interesting properties, such as electron andhole mobility and ambipolar effect. In this sense, titanium dioxide (TiO2)is a promising insulator material which adapted with graphene could lead tobetter performance of graphene based devices. In this work [1], we manufacturedthree Graphene Field Effect Transistors (GFETs) using a thin deposit of TiO­2as the dielectric layer. Characterization of the devices was done by measuringresistance between electrodes vs gate voltage, data was then fitted to themodel proposed in the literature [2] taking electron/hole mobility, contactresistance and charge carrier density as adjusting parameters. We observedthat, due to the high dielectric constant (14.0 [3]) of the TiO2,the Dirac voltage or charge neutrality point of our three GFETs has beendecreased to nearly 0V in the gate, compared to other similar devices which useSiO2 (dielectric constant of 3.8 [4]), with the Dirac voltage appearingat nearly -15V. Thus, the device being able to show the ambipolar effect atvery low voltages applied in the gate, as shown in Figure 1.  We also show that it is possible to manufactureGFETs with good electron and hole mobility values (up to 1870 cm2/Vs)using a large graphene area channel (300x300 µm2), knowing that itconveys a greater number of defects and wrinkles, generally. Photographs of themanufactured devices are shown in Figure 2. Finally, it is presented aqualitative description of the electron and hole mobilities behavior independence of the roughness of the dielectric layer, finding these mobilitiesto be decreased as the roughness increases, as expected; and thus determiningthat the dielectric layer roughness is an important parameter which couldintroduce large undesirable effects in the device performance.