Characterizations of realized metal-insulator-silicon-insulator-metal waveguides and nanochannel fabrication via insulator removal

Abstract

We investigate experimentally metal-insulator-silicon-insulator-metal (MISIM) waveguides that are fabricated by using fully standard CMOS technology. They are hybrid plasmonic waveguides, and they have a feature that their insulator is replaceable with functional material. We explain a fabrication process for them and discuss fabrication results based on 8-inch silicon-on-insulator wafers. We measured the propagation characteristics of the MISIM waveguides that were actually fabricated to be connected to Si photonic waveguides through symmetric and asymmetric couplers. When incident light from an optical source has transverse electric (TE) polarization and its wavelength is 1318 or 1554 nm, their propagation losses are between 0.2 and 0.3 dB/μm. Excess losses due to the symmetric couplers are around 0.5 dB, which are smaller than those due to the asymmetric couplers. Additional measurement results indicate that the MISIM waveguide supports a TE-polarized hybrid plasmonic mode. Finally, we explain a process of removing the insulator without affecting the remaining MISIM structure to fabricate ~30-nm-wide nanochannels which may be filled with functional material.

Experimental investigation of plasmofluidic waveguides

“…On the whole, the propagation loss for w S ¼ 190 nm is smaller than that for w S ¼ 160 nm. Similar to the previous observation, 23 this is caused by the fact that the narrower the Si strip is, the more strongly the hybrid plasmonic mode is confined in the channels. As n l increases, the propagation loss decreases.…”

“…Metal-insulator-silicon-insulator-metal (MISIM) waveguides are such hybrid plasmonic waveguides which are realized by using standard complementary metaloxide-semiconductor (CMOS) technology. [13][14][15][16][17][18][19][20][21][22][23][24] A variety of passive MISIM waveguide devices have been realized. [18][19][20]23,24 For active MISIM waveguide devices, it was experimentally demonstrated that the phase of the MISIM waveguide mode can be tuned by depleting or accumulating electrons in the silicon strip of a MISIM waveguide.…”

“…The insulator of the MISIM waveguide, which we have been studying, is not covered by metal. [22][23][24] Hence, it can be removed such that very narrow channels of width 30 nm remain to be filled with fluid. Since this MISIM waveguide mode is substantially confined in the fluid, the interaction between light and the fluid is significantly enhanced.…”

“…Previously, a mixture of buffered oxide etch (BOE) solution (Model 1178-03, JT Baker) and glycerol with a weight ratio of 2:1 had been employed for the etching to reduce Cu corrosion. 23 However, it was found that quick etching with only the BOE solution is better for the properties of the plasmofluidic waveguides than slow etching with the mixture. Hence, the chip was immersed into the BOE solution for 55 s, thoroughly rinsed with deionized water, and dried.…”

“…The relation of the insertion loss to l P fluctuates around the straight line partly due to the Fabry-Perot resonance of the 15-mm-long chip itself. 23 The slope of the straight line is the propagation loss of the plasmofluidic waveguide, and the y-intercept of the straight line corresponds to two times the coupling loss of the tapering region.…”