Thin Film High-k Dielectric Materials Development
Many emerging applications demand larger format, smaller size IRFPAs (infrared focal plane) to achieve higher resolution and wider fields of view (FOV), without sacrificing existing performance, which has presented a tremendous problem for today’s readout integrated circuit (ROIC) technology. The challenge is how to implement sufficient well capacity in small pixel pitch to meet sensitivity and intra-scene dynamic range requirements. Current ROICs are analog with integration capacitor taking up most of the pixel area. The ROIC designs are fabricated using the commercially available 250nm or 180nm CMOS (complementary metal-oxide-semiconductor) foundry process. Capacitors are implemented by laying poly over diffusion, poly over poly, metal over poly, or metal over metal with a thin layer of oxide grown between the two plates. To achieve higher charge capacitance density, the method of implementing MOS capacitor (using the thinner MOSFET gate oxides) is commonly used. Some foundry processes have processing options to stack MIM (Metal Insulator Metal) capacitors and/or tolerate higher voltage operations (translating into larger voltage swings) which allows for increased charge density. These standard foundry processes typically yield charge capacitive density of 4fF/um2- 6fF/um2. As we drive to smaller pixels, SiO2 can no longer meet the ROIC charge storage requirements.
MicroSol Technologies Inc. developed an innovative nanolaminated high dielectric material using Atomic Layer Deposition (ALD). The process flow is compatible with 250nm and 180nm CMOS technologies with a thermal budget lower than 350°C, and chemistries used in the process present no concerns for CMOS processing. The MIM characterization shows that the nanolaminated high k materials yield higher capacitance density with lower leakage current. The reproducibility of capacitance density showed a non-uniformity of approximately 5%. MIM capacitor long-term reliability was characterized by time dependent dielectric breakdown (TDDB) with a lifetime of more than 10 years for nanolaminated high-k’s.