Low temperature IC-compatible wafer-to-wafer bonding with embedded micro channels for integrated sensing systems

In this work, a low temperature wafer-to-wafer bonding technique is demonstrated. The technology can be implemented on a variety of materials serving as planar substrates in the microelectronics industry. As an integral part of this technique, one of the wafers to be bonded contains a patterned micro molded layer on the surface with a thickness range of 2 μm to 250 μm. The patterned layer serves three important purposes. First, the surface of the layer represents the bonding surface to which the second wafer is bonded. Second, the patterned areas serve as integral components of the micromachined sensor/actuator (e.g. dielectric spacers, diaphragm spacers, micro channels, reservoirs). Third, the open channels are needed as part of the fabrication sequence for the bonding process. The bonding layer on each wafer consists of a polyimide material. The patterned layer is a photosensitive polyimide material defined using conventional photolithographic techniques. The bonding layer on the second wafer is a thin film (0.5 μm -2.0 μm) of polyimide material. The polyimide layers are cured to specific degrees and aligned together before final cure and bonding. The bonding technique can be utilized in the fabrication of micromachined sensors/actuators as well as a post processing step to integrated circuit fabrication. Therefore, micromachined systems can be realized utilizing micro sensors/actuators and the integrated circuits required for signal processing, communication, and control