Limits...
Integrating metal-oxide-decorated CNT networks with a CMOS readout in a gas sensor.

Lee H, Lee S, Kim DH, Perello D, Park YJ, Hong SH, Yun M, Kim S - Sensors (Basel) (2012)

Bottom Line: The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy.The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way.The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, Seoul National University, Seoul, Korea. hyunjoong.lee@amic.snu.ac.kr

ABSTRACT
We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures.

Show MeSH
The reference resistor string. Each resistor RES[] is 20 kΩ, permitting the resistance to be dynamically varied from 20 kΩ to 320 kΩ in 20 kΩ steps.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3376610&req=5

f7-sensors-12-02582: The reference resistor string. Each resistor RES[] is 20 kΩ, permitting the resistance to be dynamically varied from 20 kΩ to 320 kΩ in 20 kΩ steps.

Mentions: Figure 7 shows the on-chip reference string of 20 kΩ resistors. Its overall resistance can be set from 20 kΩ to 320 kΩ, in steps of 20 kΩ, by an externally supplied 4-bit code, REFRSEL[0:3]. Figure 8 shows the analog front-end circuit of the CNT ROIC. An op-amp and a PMOS transistor maintain the voltage at nodes A and B at VRef3. When the INIT signal is high, the capacitors CREF and CCNT are discharged and the voltage at nodes C and D becomes VRef1. When the INIT signal goes low, two capacitors are charged and the voltages at nodes C and D increase, but the rates at which the voltages at C and D increase are different because the CNT network and the reference resistor can be expected to have different resistances. When the voltage at either node reaches VRef2, the START signal goes high; and when the second node also reaches VRef2, the STOP signal goes high. The TDIFF signal which controls the clock cycle counter goes high with the START signal, and then goes low again when the STOP signal goes high. The clock cycle counter and the DLL-based TDC together convert the time of the between arrival of the START and STOP signals to a digital code. These circuits will be discussed at next section. The SIGN signal indicates whether node C or node D reached VRef2 first. If it was C, then the SIGN signal is high, but if it was D the SIGN signal is low. This SIGN signal and the encoded 12-bit output data can be used by the program in a controller or PC to determine the resistance of the CNT network at a selected cell.


Integrating metal-oxide-decorated CNT networks with a CMOS readout in a gas sensor.

Lee H, Lee S, Kim DH, Perello D, Park YJ, Hong SH, Yun M, Kim S - Sensors (Basel) (2012)

The reference resistor string. Each resistor RES[] is 20 kΩ, permitting the resistance to be dynamically varied from 20 kΩ to 320 kΩ in 20 kΩ steps.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376610&req=5

f7-sensors-12-02582: The reference resistor string. Each resistor RES[] is 20 kΩ, permitting the resistance to be dynamically varied from 20 kΩ to 320 kΩ in 20 kΩ steps.
Mentions: Figure 7 shows the on-chip reference string of 20 kΩ resistors. Its overall resistance can be set from 20 kΩ to 320 kΩ, in steps of 20 kΩ, by an externally supplied 4-bit code, REFRSEL[0:3]. Figure 8 shows the analog front-end circuit of the CNT ROIC. An op-amp and a PMOS transistor maintain the voltage at nodes A and B at VRef3. When the INIT signal is high, the capacitors CREF and CCNT are discharged and the voltage at nodes C and D becomes VRef1. When the INIT signal goes low, two capacitors are charged and the voltages at nodes C and D increase, but the rates at which the voltages at C and D increase are different because the CNT network and the reference resistor can be expected to have different resistances. When the voltage at either node reaches VRef2, the START signal goes high; and when the second node also reaches VRef2, the STOP signal goes high. The TDIFF signal which controls the clock cycle counter goes high with the START signal, and then goes low again when the STOP signal goes high. The clock cycle counter and the DLL-based TDC together convert the time of the between arrival of the START and STOP signals to a digital code. These circuits will be discussed at next section. The SIGN signal indicates whether node C or node D reached VRef2 first. If it was C, then the SIGN signal is high, but if it was D the SIGN signal is low. This SIGN signal and the encoded 12-bit output data can be used by the program in a controller or PC to determine the resistance of the CNT network at a selected cell.

Bottom Line: The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy.The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way.The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, Seoul National University, Seoul, Korea. hyunjoong.lee@amic.snu.ac.kr

ABSTRACT
We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures.

Show MeSH