5510 IEEE SENSORS JOURNAL, VOL. 15, NO. 10, OCTOBER 2015 Cantilever-Based Dielectric Breakdown Mediated Ionization Pressure Sensor Using Poly Si Microtip Tania Mukherjee and Ambarish Paul Abstract—We report the development of cantilever-based cold cathode ionization pressure sensor that works on the principle of dielectric breakdown of gaseous medium. The high electric field ( E m = 1 MV/m) developed at the corners of the microtip produced dielectric breakdown of the medium, sufficient to produce ionization current at a relatively low bias voltage V b < 10 V. With increase in pressure, the availability of molecules in the vicinity of the micro-tip increased which when ionized by the application of V b , produced enhanced ionization current through the device. The devices with cantilever lengths L = 50, 150, 250, 350, and 450 μm were designed with interelectrode spacing ( d int ) of 1250 nm, which was further reduced by the application of suitable V b to enhance the sensor performance. The device with L = 450 μm provides the widest dynamic range of 10 -4 - 10 2 mbar and the highest sensitivity of 2.44 μA/mbar with power consumption of 1.32 × 10 -1 μW at 10 V, which is 10 4 times lower than previously reported device. The device offers a service life of 60 cycles assuming a tolerance of 10% in device performance. Index Terms— Dielectric breakdown, spring constant, field emission, sensor, ionization. I. I NTRODUCTION V ARIOUS groups have explored ionization based devices as pressure sensors [1]–[7]. Although the use of ioniza- tion sensors are limited by its huge size, bulky architecture, high power consumption and risky high voltage operation, they provide 10 3 times wider dynamic range than the capacitive [8]–[11], piezo resistive [12], [13] and thermo- resistive [14]–[20] based sensors. The ionization based devices work on the principle of impact ionization [6], which occurs when highly energetic electrons emitted from the cathode knock out electrons from the valence shell of the gas atoms, leading to their ionized state. The ionization devices are classified into hot and cold cathode type devices where energetic electrons are generated due to thermo-ionic [21] and field emission (FE) [3] respectively. Since thermionic emission occurs at high temperatures of 1000 °C, hot cathode devices suffers from outgassing problem [21]. Thus, the cold Manuscript received April 23, 2015; revised May 21, 2015; accepted May 24, 2015. Date of publication July 2, 2015; date of current version August 6, 2015. This work was supported in part by Indian Space Research Organisation, Government of India, and in part by the Ministry of Human Resource Development, Government of India. The associate editor coor- dinating the review of this paper and approving it for publication was Prof. Weileun Fang. The authors are with the Advanced Technology Development Centre, IIT Kharagpur, Kharagpur 721302, India (e-mail: taniamukherhee@ iitkgp.ac.in; ambarish@iitkgp.ac.in). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2015.2442273 cathode ionization (CCI) devices are preferred over their hot cathode counterpart. Researchers designed devices of varied architecture to achieve wide dynamic range and low power consumption in ionization sensors. The devices were realized by bulk micro-machining technique (BMT) [6] where the substrates were selectively etched to generate three dimensional structures. Baptist et al. [21] used BMT to develop the first CCI based pressure sensor. The device was bulky and complex in design with micro-tips on one of the four electrodes. With an inter electrode spacing (d int ) of 2.2×10 7 nm, the device operated on bias voltage (V b ) of 500 V, consumed power of 2×10 4 μW and exhibited a dynamic range of 10 -11 -10 -3 mbar. With the advent of improved micro- machining process, Kim [22] used a two electrode device and CNT as electron emitter to reduce the d int to 5×10 5 nm. Although this device was portable and simple in design, it suffered from high V b of 1000 V, high power consumption of 1×10 5 μW and narrow dynamic range of 10 -3 -10 -1 mbar. To improve the device performance, Choi and Woo [23] developed a three electrode device with separate emission and ionization chambers to reduce the V b to 200 V and power consumption to 2.3×10 3 μW and improved the dynamic range to 10 -4 -1 mbar. In order to enhance the sensor performance, the device structure grew increasingly complex with the incorporation of more number of electrodes. Inspite of the flexibility of BMT to fabricate devices with complex architecture, it suffered from limitations in fabrication processes which failed to reduce d int below 3×10 5 nm leading to risky high V b operation and high power consumption. To overcome the limitations of BMT, the researchers introduced surface micro-machining technique (SMT) where devices are fabricated by subsequent processes of thin film deposition and etching [24], [25]. Recent advancements in SMT facilitated the researchers to reduce the device dimen- sions significantly and develop miniaturized devices with d int of 700 nm [26]. Capacitive [27]–[30], piezo-resistive [12], thermo-electric [31]–[35] and resonant [36] type pressure sen- sors were developed using this technique. Despite progresses in modern fabrication facilities, pressure sensors developed so far using SMT suffer from low sensitivity and narrow dynamic range. Thus we propose a surface micro-machined ionization based pressure sensor which operates at low V b and offers improved sensitivity and dynamic range. In this paper, we report the development of cantilever type dielectric breakdown mediated CCI pressure sensor for the first time. In previously reported ionization based 1530-437X © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.