BACKGROUND:  Terahertz radiation sources are a highly sought after technology within imaging and diagnostic circles. Because the radiation produced from these sources is non-ionizing, as opposed to x-rays, they can be used in medical and security imaging applications without worrying about injury. One way to manufacture these sources is through stacking thin gallium arsenide (GaAs) layers at different crystal orientations on top of one another, which then enable the production of the radiation via nonlinear frequency conversion of commercial lasers. Bonding the layers together is a difficult procedure though, often requiring high pressures and temperatures to eliminate voids and provide adequate bonds of the layers. The high pressures limit the overall size of the bond area, and the high temperatures cause source performance degradation. Intermediate adhesion layers have been identified which allow for manufacturing processes that use lower temperatures and pressures, but previously these layers introduce significant losses, which reduce the source output.

INNOVATION:  Researchers at UCLA have discovered a method to produce large-area wafer bonding of GaAs wafers through low pressure and low temperature methods by using Teflon as an intermediate adhesion layer. Teflon overcomes the losses typically seen in intermediary bonding layers because it has high optical transmission in the terahertz regime, yet still serves as a very successful bonding agent. The low glass transition temperature of Teflon enables low pressure and low temperature manufacturing processes, which allow the fabrication of large area bond stacks.

POTENTIAL APPLICATIONS 

• Source of terahertz (THz, T-ray) radiation
• Medical diagnostics
• Dental imaging
• Security screening
• High altitude telecommunications

ADVANTAGES

• Low temperature, low pressure method to produce stacks of GaAs wafers
• Lower processing temperatures compared to diffusion bonding
• High optical transmission, i.e. low loss, compared to eutectic-metal bonding
• Low pressure technique enables large area (1-100 cm2) fabrication

DEVELOPMENT-TO-DATE:  Bonding of wafers and successful generation of terahertz radiation has been demonstrated.

Reference: UCLA Case No. 2008-376