The field of flexible electronics is receiving considerable attention from scientific and industrial communities because of its potential impact on a wide variety of applications including wearable audio systems, flexible photovoltaics, flexible RFID tags, flexible biomedical sensors, flexible displays, and flexible loudspeakers, which cannot be addressed by conventional wafer-based electronics. One of the most promising device developed for the flexible electronics technology are the amorphous Indium-Gallium-Zink-Oxide thin-film transistors (a-IGZO TFT). These devices show interesting electrical characteristics and can be fabricated at low temperatures. These features allow the implementation of a-IGZO TFTs on flexible substrates such as plastic foil or paper, and also enables cost effective manufacturing. The development of systems on a chip (SOC), system in a package (SIP), organic and large-area electronics (OLAE), and electronics on unconventional substrates has become an interesting research area nowadays, mainly due to the inevitable down-scaling limit on silicon-based electronic devices which has led to the transition from the era of Moore’s law to the beyond Moore era. This thesis presents two major ideas: First, a development of a SPICE model for a-IGZO TFTs, and second being design of TFT amplifier circuits targeting flexible electronics applications, using the developed model. To enable such applications with a-IGZO TFTs, the development of analog processing circuits, such as amplifiers, oscillators, and data converters, are needed. As the first step toward the development of flexible electronics applications, subsystems like motion and temperature sensors, analog and radio frequency (RF) circuits are designed. Prior to the fabrication of these circuits, a set of design rule checks (DRCs) were performed for manufacturability. These DRCs guarantee the functionality of the circuits even when the flexible substrates are bent to a radius of 5 mm. Several amplifiers with different topologies were fabricated using this process. Some topologies like Cherry-Hooper amplifier and amplifier using inductive peaking technique are developed for the first time in TFT technology. The Cherry-Hooper amplifier in particular exhibited a 3 dB bandwidth of 3.5 MHz, thereby demonstrating operation in the megahertz regime.