3596 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 60, NO. 10, OCTOBER 2013 Comparative Leakage Analysis of GeOI FinFET and Ge Bulk FinFET Vita Pi-Ho Hu, Member, IEEE, Ming-Long Fan, Student Member, IEEE, Pin Su, Member, IEEE, and Ching-Te Chuang, Fellow, IEEE Abstract— We present a comparative leakage analysis of germanium-on-insulator (GeOI) FinFET and germanium on bulk substrate FinFET (Ge bulk FinFET) at device and circuit levels. Band-to-band tunneling (BTBT) leakage-induced bipolar effect is found to result in an amplified BTBT leakage for GeOI FinFET. Device and circuit designs to mitigate the amplified BTBT leakage of GeOI FinFETs are suggested. The effectiveness of various high threshold voltage technology options including increasing channel doping, increasing gate length and drain-side underlap for leakage reduction is analyzed. Index Terms— Band-to-band tunneling (BTBT) leakage, FinFET, germanium, germanium-on-insulator (GeOI). I. I NTRODUCTION F inFET has emerged as the prime candidate for extremely scaled MOSFETs due to its superior control of short- channel effects (SCEs) [1]–[3]. Germanium device offers high mobility [4]–[8]. However, due to its high permittivity and low bandgap, germanium device suffers from SCE and severe band-to-band tunneling (BTBT) leakage. Combining the advantages of the FinFET structure and the high mobility of Ge becomes a promising approach for future high-performance MOSFETs [9]–[12]. Si-on-insulator (SOI) FinFET and Si bulk FinFET have been studied [13]–[15], and the results showed that Si FinFET on bulk substrate with an optimized punch through stopper (PTS) doping [16] underneath the channel region can exhibit comparable performance and leakage with that on SOI substrate. However, a comparative leakage analysis between germanium-on-insulator (GeOI) FinFET and Ge bulk FinFET has rarely been seen. In this work, the BTBT leakage current in the GeOI FinFET is shown to be amplified due to the bipolar effect, and various device design strategies for mitigating the bipolar gain (β) and leakage current of GeOI FinFETs are examined. This work is organized as follows. Section II describes the device design, simulation methodology, and device characteristics. Section III investigates the device and circuit designs to suppress the Manuscript received April 17, 2013; accepted August 7, 2013. Date of publication September 4, 2013; date of current version September 18, 2013. This work was supported in part by the National Science Council of Taiwan under Contract NSC 100-2628-E-009-024-MY2 and Contract NSC 102-2911- I-009-302 (I-RiCE), and in part by the Ministry of Education in Taiwan under ATU Program. The review of this brief was arranged by Editor W. Tsai. The authors are with the Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 30010, Taiwan (e-mail: vitabee.ee93g@nctu.edu.tw; pinsu@faculty.nctu.edu.tw). 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.2013.2278032 Fig. 1. Schematic view of GeOI and Ge bulk FinFETs, and device parameters used in this work. For Ge bulk FinFET, the PTS doping (N PTS ) is adjusted to have comparable subthreshold swing compared with the GeOI FinFET. FinFETs GeOI 1E-7 1E-5 A) Ge Bulk Vds=1V,0.05V 1E-9 1E-3 Vth+1V ( μA/μ m) Experimental data TCAD Ids(A 1E-11 -1.2 -1.0 -0.8 -0.6 -0.4 1E-5 1E-4 Ileak@Vgs=V Vds (V) pFET 0.0 0.2 0.4 0.6 0.8 1.0 Vgs(V) Fig. 2. I ds versus V gs characteristics of GeOI and Ge bulk FinFETs. Ge bulk FinFET uses PTS to control the subthreshold leakage. GeOI FinFET shows different I off compared with the Ge bulk FinFET at V ds = 1 V. Inset: BTBT leakage current calibration at various V ds [19]. amplified BTBT leakage due to the BTBT-induced bipolar effect. Section IV is the conclusion. II. DEVICE DESIGN AND TCAD SIMULATION METHODOLOGY Fig. 1 shows the schematics of the GeOI and Ge bulk FinFETs and the device parameters used in this work. The PTS doping (N PTS ) of the Ge bulk FinFET is adjusted to have comparable subthreshold swing compared with the GeOI FinFET, as shown in Fig. 2. 0018-9383 © 2013 IEEE