The development of a cheap, fast and versatile device able to control the air breathed in the Italian and international metropolitans has been become year by year more crucial for human health. In this thesis work, an ultra-low consumption chemo-resistive gas sensor has been developed based on the Micro and Electro-Mechanical system (MEMs) technology. This result has been achieved tuning as well as possible the electrical features of the micro-heater and the thermal response of the overall structure, splitting the process to investigate which layout and structure configuration are the best one. Meander, spiral and closed layouts have been produced on rectangular and square membranes, and they have been compared by power efficiency, temperature distribution, parasitic currents, mechanical stability and ageing. Also, suspended and bridges membrane configurations have been developed, investigating which one has the best process efficiency, mechanical properties and the lowest thermal dissipation. The bridge-membrane configuration has been improved by frontal cuts to develop an empirical relation between the TMAH etching time and the presence of these added features; also, this configuration has been intensely investigated for its impressive frontal etching results. Electrical and mechanical characterisations have been carried out on each micro-heater layout, and a ranking has been produced which spiral layout leads with an astonishing low power consumption of 37 mW. Interesting are also the results that have been found out by the mechanical testing, which has suggested that not all the membrane produced are compatible with the bridge-configuration. To commercialize the device, also the bonding must be tested by shear and pull tests, and the results are well above the limit permitted by law. The final gas characterisation has been performed on the devices with the most widely used sensible material (SnO2), and all the gas sensors tested have been worked properly. The goal of this thesis work has been achieved successfully with the production of a cheap, portable, versatile and low-power consumption chemo-resistive gas sensor able to detect selectively hazardous species for human health in air. Further, a possible trend for the future could be the decreasing of the overall dimension until up 1.5*1.5 μm2, to have a higher number of devices on each wafer (from 2100 to 5800) and, for that, higher economic profit.
Lo sviluppo di un dispositivo economico, veloce e versatile capace di controllare l’aria respirata nelle metropolitane italiane ed internazionali è diventato sempre più essenziale per la salute umana anno dopo anno. In questo lavoro, un sensore di gas chemo-resistivo a basso consumo è stato sviluppato tramite alla tecnologia MEMS. È stato possibile raggiungere questo obiettivo grazie all’ottimizzazione delle caratteriste elettriche del micro-riscaldatore e dell’isolamento termico dell’intera struttura, modificando il processo per capire e studiare quale layout e quale tipo di configurazione fosse la migliore. Su membrana rettangolare e quadrata i layout a serpentina, spirale e a geometria chiusa sono stati prodotti, sono stati inoltre confrontati in base all’efficienza energetica, alla distribuzione della temperatura, alle correnti parassite, alla stabilità meccanica e alla resistenza all’invecchiamento. Due sono le configurazioni testate durante questo lavoro: membrana sospesa e membrana con ponti, queste sono state studiate per trovare la migliore nell’efficienza di processo, nelle proprietà meccaniche e quella con la minor dissipazione termica. La configurazione a ponti è stata inoltre migliorata con dei tagli frontali per migliorare e velocizzare l’attacco di etching tramite TMAH, concentrandosi, inoltre, su quali fossero i piani cristallini coinvolti in questo attacco chimico. Test elettrici e meccanici sono stati effettuati su ciascun layout e, per definire quale fosse il migliore per questa applicazione, una classifica è stata stilata che sentenzia il micro-riscaldatore a spirale come migliore, con un consumo di soli 37 mW. Interessanti sono anche i risultati dei test meccanici, infatti questi dimostrano che non tutti i layout sono compatibili con la configurazione a ponti. Per poter commercializzare questo sensore di gas anche i bondaggi effettuati devono essere testati e i valori di resistenza di pull and shear devono essere maggiori di un minimo richiesto da legge. L’ultima caratterizzazione effettuata è quella della funzionalità vera e propria dei sensori, sono stati testati in delle camere gas con il materiale chemo-resisitivo per eccellenza: SnO2; e tutti i sensori testati hanno risposto in maniera eccellete. Perciò l’obbiettivo di questo lavoro è stato raggiunto, producendo un dispositivo economico, portabile, versatile e con un bassissimo consumo capace di individuare selettivamente nell’aria le specie chimiche dannose per la salute. Il prossimo step sarà quello di diminuire ancora la dimensione dei sensori, fino ad arrivare a 1.5*1.5 μm2 per aver un maggior numero di dispositivi su ciascun wafer (da 2100 a 5800) e aumentare cosi anche il profitto economico.
Optimization and production of chemo-resistive gas sensors based on ultra-low power consumption silicon micro-heater
SCATTOLO, ELIA
2018/2019
Abstract
The development of a cheap, fast and versatile device able to control the air breathed in the Italian and international metropolitans has been become year by year more crucial for human health. In this thesis work, an ultra-low consumption chemo-resistive gas sensor has been developed based on the Micro and Electro-Mechanical system (MEMs) technology. This result has been achieved tuning as well as possible the electrical features of the micro-heater and the thermal response of the overall structure, splitting the process to investigate which layout and structure configuration are the best one. Meander, spiral and closed layouts have been produced on rectangular and square membranes, and they have been compared by power efficiency, temperature distribution, parasitic currents, mechanical stability and ageing. Also, suspended and bridges membrane configurations have been developed, investigating which one has the best process efficiency, mechanical properties and the lowest thermal dissipation. The bridge-membrane configuration has been improved by frontal cuts to develop an empirical relation between the TMAH etching time and the presence of these added features; also, this configuration has been intensely investigated for its impressive frontal etching results. Electrical and mechanical characterisations have been carried out on each micro-heater layout, and a ranking has been produced which spiral layout leads with an astonishing low power consumption of 37 mW. Interesting are also the results that have been found out by the mechanical testing, which has suggested that not all the membrane produced are compatible with the bridge-configuration. To commercialize the device, also the bonding must be tested by shear and pull tests, and the results are well above the limit permitted by law. The final gas characterisation has been performed on the devices with the most widely used sensible material (SnO2), and all the gas sensors tested have been worked properly. The goal of this thesis work has been achieved successfully with the production of a cheap, portable, versatile and low-power consumption chemo-resistive gas sensor able to detect selectively hazardous species for human health in air. Further, a possible trend for the future could be the decreasing of the overall dimension until up 1.5*1.5 μm2, to have a higher number of devices on each wafer (from 2100 to 5800) and, for that, higher economic profit.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/150001