Leakage current behavior was investigated for diode-connected low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) with the coplanar structure for electrostatic discharge (ESD) protection in display product with high luminance backlight system. In this study, the bottom metal (BM) layer was adopted to block lights coming from backlight system. We observed different leakage current behaviors as each other electrical connection of BM layer, such as floating BM (FBM), source-contacted BM (SBM), and gate-contacted BM (GBM). In particular, when negative voltage is applied, LTPS diodes with SBM and FBM show the high leakage current by increasing current flow through back-channel. On the other hand, GBM has comparable low leakage current with non-BM. These leakage current characteristics were verified by technology computer-aided design (TCAD) simulation.