Precursor to Gas Sensor: A Detailed Study of the Suitability of Copper Complexes as an MOCVD Precursor and their Application in Gas Sensing

Abstract

There are very few p-type semiconductors available compared to n-type semiconductors for positive sensing response for oxidizing gases and other important electronic applications. Cupric oxide (CuO) is one of the few oxides that show p-type conductivity, useful for sensing oxidizing gases. Many researchers obtained CuO using the chemical and solid-state routes, but uniformity and large-area deposition have been the main issues. Chemical vapor deposition is one such technique that provides control on several deposition parameters, which allow obtaining thin films having crystallinity and uniformity over a large area for the desired application. However, CuO-chemical vapor deposition (CVD) is still unfathomed due to the lack of suitability of copper precursors based on vapor pressure, contamination, and toxicity. Here, to address these issues, we have taken four Cu complexes (copper­(II) acetylacetonate, copper­(II) bis­(2,2,6,6-tetramethyl-3,5-heptanedionato), copper­(II) ethylacetoacetate, and copper­(II) tert-butylacetoacetate), which are evaluated using thermogravimetry for suitability as a CVD precursor. The decomposition behavior of the complexes was also experimentally confirmed by depositing CuO thin films via CVD. Phase purity, decomposition, volatility, growth rate, and morphological characteristics of the films are investigated in detail. Analysis suggests that copper­(II) tert-butylacetoacetate has the highest vapor pressure and growth rate at a low temperature, making it the most suitable precursor for high-throughput CVD. Further, to investigate the role of these precursors, films deposited using Cu complexes were subjected to gas sensing. The CuO gas sensor fabricated on glass shows pronounced NO2 sensing. The sensing results of CuO films have been explained from the standpoint of roughness, morphology, and unpassivated bonds present on the surface of films and vapor pressure of precursors. The higher density of surface state and the lower resistivity of the Cu­(tbaoac)2 film lead to a sensor with higher responsivity and sensitivity (down to 1 ppm). These precursors can probably be utilized to improve the performance of other metal oxide gas sensors, especially Cu2O and Cu-III-O2.

Investigation of Vacancies Transport in the Bilayer of the Cu2O1–x/CuO1–y Resistive Switching Device and Effect of Growth Temperature on Memristive Switching

“…In this work, we report memristors using thin-film Cu 2 O 1– x /CuO 1– y heterojunctions. Cu-oxide naturally exists in two forms, Cu 2 O and CuO. , Both oxides are semiconductors, unintentionally doped p-type by intrinsic point defects . As we shall show, the resistance of the Cu 2 O 1– x /CuO 1– y heterostructure naturally stabilizes in a HRS and a LRS. , The states can be switched with an electric field, which forces the migration of charged copper vacancies between Cu 2 O 1– x and CuO 1– x .…”

Research Progress on Coating of Sensitive Materials for Micro-Hotplate Gas Sensor

“…Chemical vapor deposition technology can obtain gas-sensitive thin-film materials with good crystallinity, large area and fantastic uniformity by controlling the deposition parameters [ 67 ]. Using a chemical vapor deposition method, R. L. Wilson et al deposited NiO with different thicknesses on micro-hotplate.…”

CVD-deposited Cu2O thin films with a record Hall hole mobility of 263 cm2 V−1 s−1 and field-effect mobility of 0.99 cm2 V−1 s−1

“…1 Cu 2 O thin films have been used in a variety of applications, such as photovoltaics, gas sensing, thin-film transistors, photocathodes, and power electronics. 8–19 Several techniques have been used to deposit Cu 2 O, such as sputtering, thermal evaporation and pulsed laser deposition. Unfortunately, the Hall mobility and the device (TFT) performance have been inconsistent (Table 1).…”

“…The work is a significant advance for state-of-the-art p-type all-oxide electronics.power electronics. [8][9][10][11][12][13][14][15][16][17][18][19] Several techniques have been used to deposit Cu 2 O, such as sputtering, thermal evaporation and pulsed laser deposition. Unfortunately, the Hall mobility and the device (TFT) performance have been inconsistent (Table 1).…”