Micro light plates for low-power photoactivated (gas) sensors

We report a miniaturized device integrating a photoactive material with a highly efficient Light Emitting Diode light source. This so-called micro light plate configuration allows for maximizing the irradiance impinging on the photoactive material, with a minimum power consumption, excellent uniformity, and accurate control of the illumination. We demonstrate these advantages with an example application: photoactivated gas sensors with a power consumption as low as 30 μW (this is 1000 times lower than the best figures reported to date). The letter also presents a quantitative model and a set of design rules to implement it in further integrated applications

A parts per billion (ppb) sensor for NO2 with microwatt (μW) power requirements based on micro light plates

A film of gas sensitive ZnO nanoparticles has been coupled with a low-power micro light plate (μLP) to achieve a NO2-parts-per-billion conductometric gas sensor operating at room temperature. In this μLP configuration, an InGaN-based LED (emitting at 455 nm) is integrated at a few hundred nanometers distance from the sensor material, leading to sensor photoactivation with well controlled, uniform, and high irradiance conditions, and very low electrical power needs. The response curves to different NO2 concentrations as a function of the irradiance displayed a bell-like shape. Responses of 20% to 25 ppb of NO2 were already observed at irradiances of 5 mWatts·cm-2 (applying an electrical power as low as 30 μW). In the optimum illumination conditions (around 60 mWatts·cm-2, or 200 μW of electric power), responses of 94% to 25 ppb were achieved, corresponding to a lower detection limit of 1 ppb of NO2. Higher irradiance values worsened the sensor response in the parts-per-billion range of NO2 concentrations. The responses to other gases such as NH3, CO, and CH4 were much smaller, showing a certain selectivity toward NO2. The effects of humidity on the sensor response are also discussed

An LED Platform for Micropower Gas Sensors

We developed an integrated platform to build up conductometric sensors with controlled illumination. Our device contains a miniaturized indium gallium nitride (InGaN) LED as a light source, and a set of interdigitated electrodes (IDEs) in close contact with the LED. The sensor material is later deposited on top of the IDE, to monitor its resistance. In this configuration, all the light emitted by the LED is collected by the sensor material, leading to a very efficient photoexcitation. We demonstrate the effectiveness of the approach building a photoactivated gas sensor based on ZnO operating with as little as 100 μW

Micro Light Plates for Photoactivated Micro-Power Gas Sensors

In this contribution we present a highly miniaturized device that integrates a photoactive material with a highly efficient LED light source. This so-called micro light plate configuration (µLP) allows for maximizing the irradiance impinging on the photoactive material, with a minimum power consumption, excellent uniformity and accurate control of the illumination. We demonstrate that, with the µLP approach, very efficient low power gas sensors can be built, and provide a detailed analysis of the rationales behind such improvement, as well as a quantitative model and a set of design rules to implement it in further integrated applications. As a demonstrator, we will describe a NO2 gas sensor operating in the part per billion range (ppb) with microwatt (µW) power consumption. These are the best figures reported to date in conductometric metal-oxides (MOX) sensors operated with light (instead of heat) at room temperature

Top-Down Fabrication of Arrays of Vertical GaN Nanorods with Freestanding Top Contacts for Environmental Exposure

Arrays of 1D-vertically arranged gallium nitride (GaN) nanorods (NRs) are fabricated on sapphire and connected to both bottom and freestanding top contacts. This shows a fully validated top-down method to obtain ordered arrays of high-surface-to-volume elements that can be electrically interrogated and used, e.g., for sensing applications. Specifically, these will be used as highly integrated heating elements for conductometric gas sensors in self-heating operation. Detailed fabrication and processing steps involving inductively coupled plasma reactive ion etching (ICP-RIE), KOH-etching, interspace filling, and electron-beam physical vapor deposition technologies are discussed, in which they can be well adjusted and combined to obtain vertical GaN NRs as thin as 300 nm in arbitrarily large and regular arrays (e.g., 1 × 1, 3 × 3, 9 × 10 elements). These developed devices are proposed as a novel sensor platform for temperature-activated measurements that can be produced at a large scale offering low-power, and very stable temperature control

A parts per billion (ppb) sensor for NO2 with microwatt (μW) power requirements based on micro light plates

A film of gas sensitive ZnO nanoparticles has been coupled with a low-power micro light plate (μLP) to achieve a NO2-parts-per-billion conductometric gas sensor operating at room temperature. In this μLP configuration, an InGaN-based LED (emitting at 455 nm) is integrated at a few hundred nanometers distance from the sensor material, leading to sensor photoactivation with well controlled, uniform, and high irradiance conditions, and very low electrical power needs. The response curves to different NO2 concentrations as a function of the irradiance displayed a bell-like shape. Responses of 20% to 25 ppb of NO2 were already observed at irradiances of 5 mWatts·cm-2 (applying an electrical power as low as 30 μW). In the optimum illumination conditions (around 60 mWatts·cm-2, or 200 μW of electric power), responses of 94% to 25 ppb were achieved, corresponding to a lower detection limit of 1 ppb of NO2. Higher irradiance values worsened the sensor response in the parts-per-billion range of NO2 concentrations. The responses to other gases such as NH3, CO, and CH4 were much smaller, showing a certain selectivity toward NO2. The effects of humidity on the sensor response are also discussed

Micro light plates for low-power photoactivated (gas) sensors

We report a miniaturized device integrating a photoactive material with a highly efficient Light Emitting Diode light source. This so-called micro light plate configuration allows for maximizing the irradiance impinging on the photoactive material, with a minimum power consumption, excellent uniformity, and accurate control of the illumination. We demonstrate these advantages with an example application: photoactivated gas sensors with a power consumption as low as 30 μW (this is 1000 times lower than the best figures reported to date). The letter also presents a quantitative model and a set of design rules to implement it in further integrated applications

Nanoscale GaN LED arrays for chip-based optical nanoscope

Since the invention of high-power gallium nitride (GaN) light-emitting diodes (LEDs), enormous investigations have been carried out in the last decade, not only to improve the material quality and device performance but also to extend their applications. InGaN/GaN LEDs have been broadly employed in general illumination and backlight units because of their higher luminous efficacy and longer lifetime compared to conventional light sources. Furthermore, several innovative optoelectronic devices have been introduced into industrial markets (e.g., high-brightness display and optical sensors in smartphones). By integrating LEDs with CMOS control electronics, matrix-addressed and individually controlled GaN microLED arrays could be realized with a display luminance of 106 cd/m2 (12 W/cm2), which is a factor of 103 higher than normal commercial displays [1]. However, their spatial resolution was still low, which resulted from the LED dimensions with pixel and pitch sizes of several micrometers. Thus, in this work, nanoscale InGaN/GaN LED arrays with individual pixel control were designed and fabricated to be integrated as a novel illumination source in a chip-based lensless microscope (i.e., ChipScope) for real-time monitoring of biological cells. The challenging 3D processing steps of the high-aspect-ratio nano-/microLED arrays have been optimized to create tiny optoelectronic modules. To fabricate the well-ordered high-aspect-ratio nano-/microstructures, a top-down approach comprising nanophotolithography and hybrid etching was employed [2]. In this case, GaN LED fins with smooth sidewalls could be realized from the sequential processes of SF6/H2-based ICP-RIE and KOH-based wet chemical etching. As top and bottom surfaces of the structures are distantly separated by about 3.5 – 5 µm, device planarization plays a critical role for the feasibility of top metal contact deposition. Thus, different polymer filling materials have been carefully investigated (e.g., photoresist, spin-on-glass, and benzocyclobutene (BCB)). Along with the device fabrication, simulations of the light emission patterns have been conducted with different conditions of the integrated materials to optimize the nanoLED designs. References J. Herrnsdorf, J. J. D. McKendry, S. Zhang, E. Xie, R. Ferreira, D. Massoubre, A. M. Zuhdi, R. K. Henderson, I. Underwood, S. Watson, A. E. Kelly, E. Gu, M. D. Dawson, “Active-matrix GaN micro light-emitting diode display with unprecedented brightness,” IEEE Transactions on Electron Devices, 62(6), 1918-1925 (2015). DOI: 10.1109/TED.2015.2416915 F. Yu, S. Yao, F. Römer, B. Witzigmann, T. Schimpke, M. Strassburg, A. Bakin, H.W. Schumacher, E. Peiner, H.S. Wasisto, A. Waag, “GaN nanowire arrays with nonpolar sidewalls for vertically integrated field-effect transistors,” Nanotechnology, 28(9), 095206 (2017). DOI: 10.1088/1361-6528/aa57b