Maximizing phonon thermal conductance for ballistic membranes

Kühn, Thomas; Maasilta, I. J.

doi:10.1088/1742-6596/92/1/012082

Cited by 13 publications

(10 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This observation agrees with calculations of low temperature thermal conductance in thin membranes, for which it is well understood that lower speed of sound results in higher thermal conductance. 30 This completely differs from the more intuitive behavior observed at room temperatures where thermal conductivity always grows with a higher speed of sound. 4 Interestingly, for all periods and thicknesses, there is a clear transition region around 100 mK to 200 mK, where the effect of the thickness with respect to the heat capacity changes sign.…”

Section: Heat Capacitymentioning

confidence: 84%

Low temperature heat capacity of phononic crystal membranes

Puurtinen

Maasilta

2016

AIP Advances

View full text Add to dashboard Cite

Phononic crystal (PnC) membranes are a promising solution to improve sensitivity of bolometric sensor devices operating at low temperatures. Previous work has concentrated only on tuning thermal conductance, but significant changes to the heat capacity are also expected due to the modification of the phonon modes. Here, we calculate the area-specific heat capacity for thin (37.5 - 300 nm) silicon and silicon nitride PnC membranes with cylindrical hole patterns of varying period, in the temperature range 1 - 350 mK. We compare the results to two- and three-dimensional Debye models, as the 3D Debye model is known to give an accurate estimate for the low-temperature heat capacity of a bulk sample. We found that thin PnC membranes do not obey the 3D Debye T3 law, nor the 2D T2 law, but have a weaker, approximately linear temperature dependence in the low temperature limit. We also found that depending on the design, the PnC patterning can either enhance or reduce the heat capacity compared to an unpatterned membrane of the same thickness. At temperatures below ∼ 100 mK, reducing the membrane thickness unintuitively increases the heat capacity for all samples studied. These observations can have significance when designing calorimetric detectors, as heat capacity is a critical parameter for the speed and sensitivity of a device.

show abstract

Section: Heat Capacitymentioning

confidence: 84%

Low temperature heat capacity of phononic crystal membranes

Puurtinen

Maasilta

2016

AIP Advances

View full text Add to dashboard Cite

show abstract

“…Therefore, the flexural mode could play a significant role in thermal transport in ultra-thin systems especially at low temperatures 42,43 . In the extreme case of graphene, this flexural mode was recently predicted to dominate the specific heat capacity and the lattice thermal conductivity 44 .…”

Section: Received Datementioning

confidence: 99%

Phonons in Slow Motion: Dispersion Relations in Ultrathin Si Membranes

et al. 2012

View full text Add to dashboard Cite

RECEIVED DATEWe report the changes in dispersion relations of hypersonic acoustic phonons in free-standing silicon membranes as thin as ~ 8 nm. We observe a reduction of the phase and group velocities of the fundamental flexural mode by more than one order of magnitude compared to bulk values. The modification of the dispersion relation in nanostructures has important consequences for noise control in nano and micro-electromechanical systems (MEMS/NEMS) as well as opto-mechanical devices.

show abstract

“…For the membrane we have P ∼ T 3.8 at the higher T range, which is fully consistent with the ballistic Rayleigh-Lamb theory, as can be seen by the nearly perfect fit of the theoretical curve. This is expected, as the cross-over from Rayleigh-Lamb modes to 3D bulk modes is estimated to take place at membrane thickness ∼ 1µm for SiN [50]. In contrast, the temperature exponents are lower for the PnC structures, around 3.0 -3.4.…”

Section: Resultsmentioning

confidence: 90%

Minimizing Coherent Thermal Conductance by Controlling the Periodicity of Two-Dimensional Phononic Crystals

et al. 2019

View full text Add to dashboard Cite

Periodic hole array phononic crystals (PnC) can strongly modify the phonon dispersion relations, and have been shown to influence thermal conductance coherently, especially at low temperatures where scattering is suppressed. One very important parameter influencing this effect is the period of the structure. Here, we measured the sub-Kelvin thermal conductance of nanofabricated PnCs with identical hole filling factors, but three different periodicities, 4, 8, and 16 µm, using superconducting tunnel junction thermometry. We found that all the measured samples can suppress thermal conductance by an order of magnitude, and have a lower thermal conductance than the previously measured smaller period, 1 µm and 2.4 µm structures. The 8 µm period PnC gives the lowest thermal conductance of all the samples above, and has the lowest specific conductance/unit heater length observed to date in PnCs. In contrast, coherent transport theory predicts that the longest period should have the lowest thermal conductance. Comparison to incoherent simulations suggests that diffusive boundary scattering is likely the mechanism behind the partial breakdown of the coherent theory.

show abstract

Maximizing phonon thermal conductance for ballistic membranes

Cited by 13 publications

References 8 publications

Low temperature heat capacity of phononic crystal membranes

Low temperature heat capacity of phononic crystal membranes

Phonons in Slow Motion: Dispersion Relations in Ultrathin Si Membranes

Minimizing Coherent Thermal Conductance by Controlling the Periodicity of Two-Dimensional Phononic Crystals

Contact Info

Product

Resources

About