CMOS temperature limit

The third microhotplate introduced in Sect. 4.3 was designed to extend the operation temperature limit imposed by the CMOS-metallization contacts in the heated area. A new heater design was devised, and a microfabrication sequence that enables the realization of Pt temperature sensors and Pt-electrodes was developed. This microhotplate was also monolithically integrated with circuitry as presented in Sect. 5.2, and operating temperatures of up to 500 °C have been achieved. 

The circular microhotplate presented in Sect. 4.1 features an upper sensor operating temperature limit of 350 °C, which is imposed by the CMOS metallization. At higher temperatures, electromigration, especially in the heater structures, will occur. 

A novel microhotplate design was proposed to overcome the CMOS operating temperature limit and to avoid polysilicon-induced drift problems. A cross-sectional schematic of the device is shovm in Fig. 4.11. Instead of using a polysilicon resistor as temperature sensor, a platinum temperature sensor is patterned on the microhotplate. The Pt-metallization process step was used to simultaneously fabricate the electrodes and the temperature sensor. The CMOS-Al/Pt contacts are located off the membrane... 

To overcome the temperature limits of CMOS integrated systems that are imposed by, e.g., the degradation of the CMOS metallization, a microhotplate with Pt-temperature sensor was also monolithically integrated with circuitry so that the hotplate operating temperature range could be extended to 500 °C (Sect. 5.2). The read-out of the comparatively low Pt temperature sensor resistance required the integration of a fully differential amplifier architecture. 

From the vantage point of microfluidics, the structures developed by Petersen et al [33] are the most appropriate. More recently, Baltes and coworkers combined CMOS circuitry with the microfabrication of sensors to construct a thermal mass flow system based on thin-film pyrometers [66]. As free standing mass flow sensors, they have attractive features. However, all of these silicon-based devices operate at relatively high temperatures in the 100-200 °C range. This elevated temperature limits their potential application in more complex microfluidic systems. The ideal flow sensor would be a very-low-temperature element that could be used on the walls of the microchannel. 

The limit for the operating temperature of CMOS-microhotplates can be extended by using the microhotplate that was presented in Sect. 4.3. We now detail high-temperature microhotplates with Pt-resistors that have been realized as a single-chip device with integrated circuitry. While the aluminum-based devices presented in Sect. 4.1 were limited to 350 °C, these improved microhotplates can be heated to temperatures up to 500 °C. As the typical resistance value of the Pt-resistor is between 50 and 100 Q, a chip architecture adapted to the low temperature sensor resistance was developed. The system performance was assessed, and chemical measurements have been performed that demonstrate the full functionality of the chip. 

Recently, Cree Research Inc. reported on the first p-channel 6H-SiC MOSFET [6]. The device structure and output characteristics are shown in FIGURES 8 and 9, respectively. The device current and transconductance are very small (76 pA mm 1 at 40 V of drain bias and 16 pS mm 1, respectively, for a 7 pm gate length device). The performance of this device was limited by a large parasitic series resistance. Nevertheless, even these preliminary results show the feasibility of SiC CMOS technology, capable of operating at elevated temperatures. 

The post-deposition of the metal-oxide sensing layer needs to be CMOS-compatible, and its post-deposition annealing is limited in terms of temperature and time. 

There is plenty of information available in literature on liquid crystalline and isotropic phases of different surfactants, but the study of the solid phases is limited to only soaps [12-19]. The basic reason for the lack of solid phase studies of synthetic surfactants is their limited use in solid form. The low KP of these surfactants limits their use to liquid products. Owing to a relatively high KP, sodium cocoyl isethionate (SCI), alkyl glycerol ether sulfonate (AGES), and sodium cocoyl monoglyceride sulfate (CMOS) form solid phases at room temperature, but there is hardly any information available on these solid phases. 

---