Research on heterojunction (HJ) metal oxide thin film transistors (TFTs) has accelerated remarkably over the last decade due to their superior performance over their conventional single-layer (SL) counterparts. Promising results in laboratory-scale demonstrations have further triggered an increased number of investigations into fabrication and processing techniques for the large-scale integration of HJ metal oxide TFTs. Nevertheless, a lack of consensus regarding the most appropriate scalable manufacturing technique, which combines low-cost and high-throughput fabrication, holds back new opportunities for HJ metal oxide TFTs in emerging applications. In this thesis, novel approaches and strategies are introduced to facilitate the large-scale integration of HJ metal oxide TFTs. The first study of this dissertation introduces the solution-processed In2O3/ZnO heterojunction TFTs with a high-κ bilayer dielectric consisting of Al2O3/ZrO2. Processing was carried out on rigid glass as well as flexible PEN substrates via rapid flash lamp annealing (FLA) as an alternative scalable and high-throughput processing route to conventional thermal annealing. In the second study of the dissertation, a novel 3D/2D/3D mixed-dimensional channel concept was developed with the combination of scalable spray coating and FLA techniques. The insertion of sprayed MoS2 nanoflakes between flashed SnO2/ZnO HJ results in outstanding device performance with a high mobility value of 62 cm2/Vs compared to single layers as well as heterojunction metal oxide TFTs, showing maximum mobility of 4.48 cm2/Vs. In the third study, the fabrication of In2O3/ZnO heterojunction metal oxide TFTs with solution-processed conductive Ti3C2Tx MXene contacts using a processing route that fully relies on a scalable spray coating process is demonstrated as an alternative to low-throughput vacuum-based electrodes. Notably, the proposed approach was successfully upscaled to a 4-inch glass substrate, underlining the significant potential garnered by MXene electrodes for industrial-scale electronics. The last study of the dissertation exploits the advantages of the adhesion-lithography (a-Lith) technique, which enables the development of coplanar self-aligned gate (SAG) In2O3/ZnO heterojunction TFTs and their facile integration into large-area electronics. Using the a-Lith technique, coplanar SAG architectures were fabricated where the gate and dielectric (Al and Al2O3, respectively) are located side by side with the source/drain electrodes (Au), separated from each other by nanogaps.