Low-temperature direct bonding of poly(methyl methacrylate) for polymer microchips

A low-temperature, direct bonding method for poly(methyl methacrylate) (PMMA) plates has been developed by employing surface treatment by atmospheric pressure oxygen plasma, vacuum oxygen plasma, ultraviolet (UV)/ozone or vacuum ultraviolet (VUV)/ozone. Reasonable bonding strength, as evaluated by a tensile test, was achieved below the glass transition temperature (T_g). The highest bonding strength among the achieved results is 1.43 MPa (about three times the value for conventional direct bonding) at an annealing temperature of 50°C and an applied pressure of 2.5 MPa for 10 min. Low-temperature bonding prevents deformation of the PMMA microstructure. A prototype PMMA microchip that has fine channels of 5μm depth was fabricated by hot-embossing using a Si mold. After atmospheric pressure oxygen plasma activation, direct bonding was carried out at an annealing temperature of 75°C and an applied pressure of 3 MPa for 3 min. The method gives good bonding characteristics without deformation and leakage. This low-temperature bonding technology can be applied to polymer micro/nano structures.