High-pressure microfluidics offers fast analyses of thermodynamic parameters for compressed process solvents. However, microfluidic platforms handling highly compressible supercritical CO 2 are difficult to control, and on-chip sensing would offer added control of the devices. Therefore, there is a need to integrate sensors into highly pressure tolerant glass chips. In this paper, thin film Pt sensors were embedded in shallow etched trenches in a glass wafer that was bonded with another glass wafer having microfluidic channels. The devices having sensors integrated into the flow channels sustained pressures up to 220 bar, typical for the operation of supercritical CO 2. No leakage from the devices could be found. Integrated temperature sensors were capable of measuring local decompression cooling effects and integrated calorimetric sensors measured flow velocities over the range 0.5-13.8 mm/s. By this, a better control of highpressure microfluidic platforms has been achieved.

In this letter, we report the theoretical study on phonon transport in monocrystalline silicon thin-film having unfilled or metal-filled circular holes (i.e., phononic crystals, PnC) and show that the thermal conductivity, 𝜅 at 1 K can be maximally reduced by using multi-scale structure which accords us control over the porosity of the structure. The circular scatterers are placed in the square (SQ) and hexagonal (HX) pattern with fixed 100 nm inter-hole spacing and the pit diameter is varied between 10 -90 nm. Each of the corresponding silicon PnC show reduced 𝜅 compared to the unpatterned film. The SQ-PnC having tungsten-filled pits shows the greatest reduction in 𝜅 when we consider only the effects of coherent scattering. Further, we have computed 𝜅 for the PnC where the unit cell, of 100 nm and 500 nm sizes, comprises the Sierpinski gasket (SG) with circular holes of different diameters (depending on the fractal order) in the same cell. It is observed that the 𝜅 for the 2 nd (100 nm cell) and 3 rd order (500 nm cell) SG-PnC are comparable to the SQ-and HX-PnC with pit diameters of 90 nm. When we add the effect of the diffuse boundary scattering in 𝜅, there is a lowering in 𝜅 compared to that when only the coherent effects are considered. The additional 𝜅-reduction due to boundary scattering for the SQ-PnC and HX-PnC (both with 90 nm dia.) as well as the 2 nd and 3 rd order SG-PnC are 47%, 40%, 80% and 60%, respectively.