Development of pyroelectric sensor integrated with two-dimensional transistor
Creators: name: Mbisike, Stephen Chukwuemeka
Publisher: name: The University of Edinburgh
Year: 2023
Subjects: pyroelectric sensor
two-dimensional transistor
complementary metal-oxide semiconductors (CMOS)
integrated circuit technology
silicon based microelectronics
Pyreos’s lead zirconium titanate (PZT)
Pyreos’s lead zirconium titanate (PZT) based pyroelectric sensor
2D tungsten diselenide (WSe2)
field effect transistor (FET)
2D tungsten diselenide (WSe2) field effect transistor (FET)

description: Progress in the complementary metal-oxide semiconductors (CMOS) integrated circuit technology and the acceptance of silicon based microelectronics have revolutionised the electronics world. Advancement in human endeavour relies on the improvement of our processes and the discovery of new materials with beneficial properties. The advent of two dimensional (2D) materials has created exciting new possibilities. Possibilities that not only include the replacement of silicon in microelectronics but also for application in other areas such as photonics. Also, the quest to move beyond silicon and its oxide has seen increased interest in potential high dielectric and/or pyroelectric materials. The primary motivation for this work is to improve the output of Pyreos’s lead zirconium titanate (PZT) based pyroelectric sensor by integrating the device with a 2D tungsten diselenide (WSe2) field effect transistor (FET). A systematic approach has been taken to realise this goal by first exploring the material properties individually. From varied literature, two dimensional (2D) materials have shown promise in both electrical and optical properties. In this work, studies have been conducted on the 2D material WSe2, which has been deposited via exfoliation and pulse laser deposition (PLD). Though PLD WSe2 offers good control during deposition, our findings show that the exfoliated WSe2 has better electrical and optical properties. The field effect mobility calculated for the exfoliated WSe2 and PLD-WSe2 FET is 12.06 cm2/Vs and 5.66 × 10-2 cm2/Vs respectively. A maskless lithography method has been employed for the fabrication of the devices and tests were carried out using a Keithley parameter analyser, Raman and photoluminescence (PL) spectroscopy. The PL spectra showed that the exfoliated WSe2 has a bandgap of 1.6 eV while the PLD WSe2 possessed no bandgap, thereby limiting its applications. We studied the breakdown characteristics of a 20 nm anodic tantalum, a potential high dielectric gate oxide. At an electric field of 1.5 MV/cm, the leakage current extracted for the as-deposited, 200 °C and 400 °C annealed anodic tantalum are 10-5, 10-2 and 1 A/cm2 respectively while the breakdown field is 5.4, 5.1 and 3.3 MV/cm respectively. Upon integration of the anodic tantalum with a WSe2 FET, a field effect mobility of 0.9 cm2V-1s-1 has been realised. Analysis has also been conducted on the PZT pyroelectric device to understand its surface profile using energy backscatter diffraction (EBSD) and a factorial design of experiment. From the EBSD analysis, the sputtered PZT possesses a grain size of about 100 nm and exists in tetragonal crystals having good correlation for an orientation along the [111] direction normal to the surface. Results and understanding from the factorial design of the experiment enabled the integration of PZT with a WSe2 FET. While the standalone PZT based sensor possesses a 1 nA/mm2 current density output, the integrated PZT based WSe2 FET has an output of 16 nA/mm2. This improvement in the overall current output is over ten orders of magnitude. Thus, we have succeeded in amplifying the output of the PZT pyroelectric based sensor. The experimental outcomes of this thesis would help the research community in developing higher performing integrated sensors and possibly exposing other areas of interest on inexpensive and simple methods for producing materials with high dielectric constants.