Design and fabrication of micro-hotplates made on a polyimide foil: electrothermal simulation and characterization to achieve power consumption in the low mW range

Abstract

The design of ultra-low power micro-hotplates on a polyimide (PI) substrate supported by thermal simulations and characterization is presented. By establishing a method for the thermal simulation of very small scale heating elements, the goal of this study was to decrease the power consumption of PI micro-hotplates to a few milliwatts to make them suitable for very low power applications. To this end, the mean heat transfer coefficients in air of the devices were extracted by finite element analysis combined with very precise thermographic measurements. A simulation model was implemented for these hotplates to investigate both the influence of their downscaling and the bulk micromachining of the polyimide substrate to lower their power consumptions. Simulations were in very good agreement with the experimental results. The main parameters influencing significantly the power consumption at such dimensions were identified and guidelines were defined allowing the design of very small (15 × 15 μm) and ultra-low power heating elements (6 mW at 300 • C). These very low power heating structures enable the realization of flexible sensors, such as gas, flow or wind sensors, for applications in autonomous wireless sensors networks or RFID applications and make them compatible with large-scale production on foil such as roll-to-roll or printing processes.

Gas Sensing Properties of Metal-decorated Tungsten Oxide Nanowires Directly Grown onto Flexible Polymeric Hotplates

“…Aerosol assisted CVD, as shown by our prior results [1,2], is a flexible, inexpensive and high-yield technique for growing metal oxides with remarkable gas sensing properties. Here we show the success of this technique in the growth of lowdimensional metal oxide nanostructures directly on flexible polymeric hotplates [3,4], e.g. suitable for integration in low cost tags.…”

“…A 700 nm thick photo-definable polyimide layer was spin-coated on the top of the heating area to electrically insulate the heater from the electrodes. And finally, interdigitated electrodes (Ti/Pt with a gap of 5μm and a square shape) were deposited on the top of the insulated film by sputtering and patterned by lift-off [3,4].…”

Design and Simulation of Parallel Microheater

“…The losses due to radiation can be neglected at the temperature range of interest of microheater and due to the very low emissivity of the materials involved (Courbat et al, 2011). Therefore Eq.…”

An Accurate and Computationally Efficient Model for Membrane-Type Circular-Symmetric Micro-Hotplates

“…Importantly, unlike [23], we have also incorporated the internal heat generation while applying the thermal energy balance to the cylindrical ring: $P_{\mathrm{\Delta }r}=p\left(2\pi r\mathrm{\Delta }r\right)t_m$ $Q_c=q_c\left(2\pi r{t}_m\right)$ $Q_{cv,\mathit{\text{top}}}+Q_{cv,\mathit{\text{bottom}}}=2h_c\left(2\pi r\mathrm{\Delta }r\right)\left(T-T_a\right)$ $Q_{\mathit{\text{rad}},\mathit{\text{top}}}+Q_{\mathit{\text{rad}},\mathit{\text{bottom}}}=2\sigma \mathit{\epsilon }\left(2\pi r\mathrm{\Delta }r\right)\left(T^4-T_a^4\right)$where p is the volumetric density of the internal heat generation (obviously p is zero in the regions which do not include heaters), σ is Stefan's Boltzmann constant, q c is the heat flux for the conduction in the radial direction, 2πr Δ rt m is the volume of the thin cylindrical ring, 2πrt m is the cross sectional area for the conduction, 2πr Δ r is the surface area for the convection and radiation, T a is the ambient temperature, ε is the average surface emissivity of the membrane and h c is the average convection heat transfer coefficient (average refers to the fact that the emissivities and convection heat transfer coefficients can be different at the top and bottom surfaces). The convection heat transfer coefficient h c is difficult to determine as it depends on different parameters (geometry, packaging, environment, … [25]); however, we mention that it must be determined prior to using our method by means of FEM simulations and/or experiments [26,27]. …”