Rebecca Peterson1,Christopher Allemang1,Tae Cho1,Julia Lenef1,Nazanin Farjam1,Jaesung Jo1,Christopher Pannier1,Eric Kazyak1,Carli Huber1,Shantam Ravan1,Mattison Rose1,Robin Rodríguez1,Kishwar Mashooq1,Orlando Trejo1,Kira Barton1,Neil Dasgupta1
University of Michigan1
Rebecca Peterson1,Christopher Allemang1,Tae Cho1,Julia Lenef1,Nazanin Farjam1,Jaesung Jo1,Christopher Pannier1,Eric Kazyak1,Carli Huber1,Shantam Ravan1,Mattison Rose1,Robin Rodríguez1,Kishwar Mashooq1,Orlando Trejo1,Kira Barton1,Neil Dasgupta1
University of Michigan1
Future flexible and large-area electronics require integration of multiple area-selective deposition processes. Conformal thin films are needed with precise control over their electronic, chemical, and structural properties. Atomic layer deposition (ALD) is a promising method for layer-by-layer growth, but realizing three-dimensionally atomically-precise patterning of high-quality electronic films has remained elusive. In this talk, I will share our collaborative results on ALD of <i>n</i>-type and <i>p</i>-type oxide semiconductor thin films along with area-selective patterning and integration with ALD-deposited dielectrics and conductors. Specifically, we have developed hybrid ALD processes that combine thermal and oxygen plasma, or hydrogen plasma and oxygen plasma to realize <i>n</i>-type zinc tin oxide or <i>p</i>-type cuprous oxide semiconductors, respectively. For the <i>n</i>-type case, we found that increasing film density by ALD deposition temperature or post-deposition anneals was critical to achieving excellent electron mobility of 22 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>. Thin film transistors (TFTs) made using ALD zinc tin oxide show excellent stability and low-voltage switching behavior at back-end-of-line-compatible thermal budgets [1]. For the <i>p</i>-type case, we use the hydrogen to oxygen plasma processes and post-deposition anneals to toggle between various film phases, from metal Cu, to degenerately <i>p</i>-type doped CuO, to semiconducting <i>p</i>-type Cu<sub>2</sub>O. We furthermore show, by x-ray absorption near-edge structure (XANES) analysis, that process tuning can control the Cu(I) versus Cu(II) fraction in the film [2]. Nonetheless, when used in TFTs, the performance of these ALD Cu<sub>2</sub>O films still lags behind that of benchmark RF-sputtered Cu<sub>2</sub>O TFTs made in our lab [3]. In the future, the Cu<sub>2</sub>O devices can be improved by reducing the gate insulator interface defect density and the source/drain contact resistance. Finally, to demonstrate the ability of these films to be integrated in nanomanufacturing we combine the ALD processes with electrohydrodynamic jet printing of polymers and solvent inks to additively and subtractively pattern our electronic films. The resulting TFTs have channel length of 4 µm, well below standard ink-jet printing resolution [4]. In the future our technologies can be further integrated to realize fully printed TFTs with sub-micron resolution that can be used in customizable functional circuits and systems on a wide range of non-planar substrates.<br/>[1] C. R. Allemang, T. H. Cho, O. Trejo, S. Ravan, R. E. Rodríguez, N. P. Dasgupta, and R. L. Peterson, <i>Advanced Electronic Materials</i> <b>6</b> (7): 2000195 (2020).<br/>[2] J. D. Lenef, J. Jo, O. Trejo, D. J. Mandia, R. L. Peterson, and N. P. Dasgupta, <i>Journal of Physical Chemistry C</i>, <b>125</b> (17): 9383-9390 (2021).<br/>[3] J. Jo, J. D. Lenef, K. Mashooq, O. Trejo, N. P. Dasgupta, and R. L. Peterson, <i>IEEE Transactions on Electron Devices</i>, <b>67</b> (12): 5557-5563 (2020).<br/>[4] T. H. Cho, N. Farjam, C. R. Allemang, C. Pannier, E. Kazyak, C. Huber, M. Rose, O. Trejo, R. L. Peterson, K. Barton, and N. P. Dasgupta, <i>ACS Nano</i>, <b>14</b> (12): 17262-17272 (2020).