In-Situ Temperature Measurement on CMOS Integrated Micro-Hotplates for Gas Sensing Devices

Abstract

Metal oxide gas sensors generally need to be operated at elevated temperatures, up to and above 400 °C. Following the need for miniaturization of gas sensors and implementation into smart devices such as smartphones or wireless sensor nodes, recently complementary metal-oxide-semiconductor (CMOS) process-based micro electromechanical system (MEMS) platforms (micro-hotplates, µhps) have been developed to provide Joule heating of metal oxide sensing structures on the microscale. Heating precision and possible spatial temperature distributions over the µhp are key issues potentially affecting the performance of the overall gas sensor device. In this work, we use Raman spectroscopy to directly (in-situ and in-operando) measure the temperature of CMOS-based µhps during the application of electric current for Joule heating. By monitoring the position of the Raman mode of silicon and applying the theoretical framework of anharmonic phonon softening, we demonstrate that state-of-the-art µhps are able to reach the set temperature with an error below 10%, albeit with significant spatial temperature variations on the hotplate. This work demonstrates the potential of Raman spectroscopy for in-situ and in-operando temperature measurements on Si-based devices, an aspect of high relevance for micro- and nano-electronic device producers, opening new possibilities in process and device control.

Ceramic processing and multiferroic properties of the perovskite YMnO3‐BiFeO3 binary system

“…This is most probably associated with ceramic materials being black in colour, so that strong light absorption takes place under the incident laser beam that causes local heating, and actual temperatures to be higher than nominal ones. 45 Mechanical anomalies then can be unambiguously associated with the ferroelectric phase transition that is of the R3c  Pnma type in this case. Note that additional, irreversible hardening is triggered above 650 ºC for both x=0.925 and x=0.95 compositions.…”

Low-Power Detection of Food Preservatives by a Novel Nanowire-Based Sensor Array

“…Raman spectroscopy is a non-destructive investigation technique that was already used for the characterization of the thermal properties of μHPs [73]. In this specific case, this powerful technique allowed for determination of the crystalline structure of the sensing material at micrometer size and directly synthesized on top of the hotplate.…”

Transfer Printing Technology as a Straightforward Method to Fabricate Chemical Sensors Based on Tin Dioxide Nanowires

“…The RTD ensured the correct temperature on the gas sensing substrate due to the feedback loop (GMS1). This setup has been evaluated also with Raman-based measurement technology, which has been applied to measure the temperature of the CMOS integrated microhotplate array, which has been mentioned above [24]. The GMS2 was a stainless steel box of 80 cm3 for gas flow and provides integrated electronics for operating the sensor devices inside.…”

“…No specific equipment is necessary to produce the stamp and to transfer the NWs from one substrate to the other one—those are important advantages compared to other dry transfer methods. In the next step the dry transfer method will be employed for an 8× array of “spider-like” microhotplates with a size of 80 × 80 μm2 [24], which are integrated on a CMOS chip. For this the dry transfer method will be combined with the patterned growth of SnO2 nanowires as shown in Figure 11.…”