A thin and cost-effective bi-directional loudspeaker which can reproduce high quality sound toward contrary directions simultaneously, arranged from bottom to the top, consists of a frame, a U-yoke, a first magnet, a washer, a copper cap, a second magnet, a voice coil, a diaphragm, a spacer, a spider, a dust cap and a connector disposed on lateral side of the frame. To construct a structure of a bottom-gate-type TFT, a heat relaxation layer is formed to cover a gate electrode. A base having a first side and a second side is provided at the joint, wherein the first side is connected with the flexible joint and the second side includes an adhesive for securing the base to a patient’s chest.