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Abstract— In this paper, gate all around (GAA) MOSFET with vacuum gate dielectric is proposed for the first time for improved hot carrier reliability and RF ...

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IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 60, NO. 6, JUNE 2013

Gate All Around MOSFET With Vacuum Gate Dielectric for Improved Hot Carrier Reliability and RF Performance Rajni Gautam, Member, IEEE, Manoj Saxena, Senior Member, IEEE, Radhey Shyam Gupta, Life Senior Member, IEEE, and Mridula Gupta, Senior Member, IEEE

Abstract— In this paper, gate all around (GAA) MOSFET with vacuum gate dielectric is proposed for the first time for improved hot carrier reliability and RF performance. Analog and RF performance of the GAA MOSFET with vacuum gate dielectric (GAA VacuFET) is compared with conventional GAA MOSFET with SiO2 dielectric, and it is found that GAA VacuFET is superior to SiO2 dielectric for RF high-speed applications and more immune to the hot carrier damage because of low electric field at the drain side but it has a serious drawback of low oncurrent and transconductance as compared to SiO2 dielectric. In order to enhance the on current and transconductance of GAA VacuFET, Gate Electrode engineering and channel doping engineering are used. An analytical model is developed for dual material gate graded channel GAA MOSFET with vacuum gate dielectric (DMG GC VacuFET) and the model is verified with the simulated results. Incorporation of DMG and GC not only enhances digital and analog RF performance of GAA VacuFET but also hot carrier reliability is improved. Index Terms— Device simulation, gate all around (GAA) MOSFET, hot carrier reliability, localized charges, RF performance, symmetric gate-stack.

I. I NTRODUCTION

G

ATE all around (GAA) MOSFET is one of the most promising device structures to extend the scaling of the CMOS device as it provides the best electrostatic control of the channel [1], [2]. A lot of work on analytical modeling of GAA MOSFET has been done in past [3]–[5] and research work related to analog and RF performance of GAA MOSFET has also been reported previously [6], [7] indicating that GAA MOSFET exhibit superior intrinsic RF scaling capability, and are suitable for low-power analog/RF applications. In MOSFETs, the hot carrier-induced degradation [8], [9] resulting from impact ionization in the channel Manuscript received October 22, 2012; revised March 20, 2013; accepted April 1, 2013. Date of publication April 29, 2013; date of current version May 16, 2013. The review of this paper was arranged by Editor W. Tsai. R. Gautam and M. Gupta are with Department of Electronic Science, University of Delhi, New Delhi 110007, India (e-mail: [email protected]; [email protected]). M. Saxena is with the Department of Electronics, Deen Dayal Upadhyaya College, University of Delhi, New Delhi 110015, India (e-mail: [email protected]). R. S. Gupta is with the Department of Electronics and Communication Engineering, Maharaja Agrasen Institute of Technology, New Delhi 110086, India (e-mail: rsgup[email protected]). 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/TED.2013.2256912

near the drain junction, becomes a major reliability concern. A lot of work has been done to study the degradation due to hot carrier-induced traps/charges on the performance of the surrounding gate or gate all around (GAA) MOSFET [10], [11]. Hot carrier-induced traps in the dielectric change the device parameters, such as threshold voltage, subthreshold slope, transconductance, and carrier mobility. Therefore, study of hot carrier reliability is necessary and to explore the suitable replacement for the SiO2 dielectric is very important. FET with vacuum gate dielectric was recently proposed by Han et al. [12] where vacuum gate dielectric is formed by a sacrificial layer deposition and removal process [12], [13], and is found to be resistant to radiation and stress damage because of the absence of solid material [12]. As far as fabrication of GAA VacuFET is concerned, well established and mature techniques (top-down and bottom-up) are available in the literature for fabrication of GAA MOSFET [14]. Han et al. [12] fabricated VacuFET using sacrificial layer deposition and removal process [12], [13]. Vacuum gate dielectric was attained by complete removal of the SiO2 sacrificial layer and measurement of the device under a vacuum ambient (

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