Latent Noise in Schottky Barrier MOSFET

1. UPoN 2008 Latent Noise in Schottky Barrier MOSFET Sheng-Pin Yeh, Chun-Hsing Shih*, Jeng Gong, and Chenhsin Lien Institute of Electronics Engineering, National Tsing Hua University, Taiwan *Department of Electrical Engineering, Yuan Ze University, Taiwan *Email: chshih@saturn.yzu.edu.tw UPoN 2008

2. Latent Noise in Schottky Barrier MOSFET • Necessity of Metallic Source/Drain • I-V Curves of SBMOS • Noise in SBMOS and MOSFET • Latent Noise Mechanisms in SBMOS • Summary UPoN 2008

3. Gate Xj Rsd S/D Necessity of Metallic Source/Drain Gate Length SDE Resistance SDE Depth Source: ITRS Unacceptable SDE resistance will limit the use of impurity doped S/D UPoN 2008

4. Recent Research of SBMOS Eliminating the limits on the dopant source/drain junctions makes metallic S/D SBMOS as one of the most attracting candidates for use in future CMOS devices. UPoN 2008

5. Latent Noise in Schottky Barrier MOSFET • Necessity of Metallic Source/Drain • I-V Curves of SBMOS • Noise in SBMOS and MOSFET • Latent Noise Mechanisms in SBMOS • Summary UPoN 2008

6. SBMOS vs. MOSFET (Drain Current) Lg = 90 nm, Tox = 2.5 nm, SBH = 0.4 eV SBMOS suffers from potential constraints on the drain currents because of its unique Schottky barrier source/drain junctions. UPoN 2008

7. SBMOS vs. MOSFET (Energy Band Diagrams) SBMOS MOSFET Thermal Emission Vg= 0V Vg= 0V e- e- φBn Vg= 1V Vg= 1V SB Tunneling Vd= 1V Vd= 1V In SBMOS, carriers can thermonicly emit over or laterally tunnel through Schottky barrier to contribute drain current.Unique Impact Ionization is observed in SBMOS. UPoN 2008

8. Ambipolar Conduction SBMOS presents the ambipolar conduction as a function of gate voltage. At a negative bias, holes can also pass through the drain Schottky barrier, forming a hole channel, yielding an undesirable drain current. And, SBH must be minimized. UPoN 2008

9. Dopant Segregated Schottky Barrier MOSFET (DS-SBMOS) Insertinga heavily doped segregation layer effectively modifies the Schottky barriers to increase the driving current and suppress the ambipolar behavior. UPoN 2008

10. Drain Interface States Generated during Metal Silicidation Formation of the metallic source/drain using silicidation brings about interface states and noise sources. Importantly, trap and detrap depend on Vg and SBH. Hole UPoN 2008

11. Latent Noise in Schottky Barrier MOSFET • Necessity of Metallic Source/Drain • I-V Curves of SBMOS • Noise in SBMOS and MOSFET • Latent Noise Mechanisms in SBMOS • Summary UPoN 2008

12. Noise in Conventional MOSFETs • For MOSFETs • Drain current fluctuates due to variations of • Number of inversion charge density ∆Qi <traps in gate oxide> (and number of inversion carriers in channel ∆N=WL∆ Qi) • Effective channel mobility ∆μeff <phonon scattering> UPoN 2008

13. Unique Noise in Schottky Barrier MOSFET NMOS, p-Si T. Asano, Jpn. J. Appl. Phys., 2002, p. 2306. Observations: 1. More Noisy in SBMOS than MOSFET 2. Unique noise observed in different metals silicidation SBMOS (SBH:PtSi = 0.85 eV, NiSi = 0.65 eV for electron) UPoN 2008

14. Unique Noise in Schottky Barrier MOSFET (Cont.) PMOS M. V. Haartman, ICNF 2005, p. 307. Observations: 1. More Noisy in SBMOS (PMOS), SBH: NiSi = 0.45 eV for hole 2. Strong dependence of noise on gate bias UPoN 2008

15. Latent Noise in Schottky Barrier MOSFET • Necessity of Metallic Source/Drain • I-V Curves of SBMOS • Noise in SBMOS and MOSFET • Latent Noise Mechanisms in SBMOS • Summary UPoN 2008

16. Vg= 0V e- φBn Vg= 1V Vd= 1V Noise Mechanisms in SBMOS: at Silicon Surface Mechanisms: 1. Number Fluctuation <traps in gate oxide> 2. Mobility Fluctuation <phonon scattering> 3. But with unique impact ionization in Source UPoN 2008

17. Interface States EC φBn Vg EF EFi Schottky Source Si EV Noise Mechanisms in SBMOS: at Source Mechanisms: 1. Trap levels in Schottky barrier contact (SBH and Gate bias dependent) 2. Trap levels in substrate metallic Source contact (SBH and substrate bias dependent) 3. Different in DS-SBMOS and SBMOS UPoN 2008

18. Noise Mechanisms in SBMOS: at Drain Mechanisms: 1. Trap levels in channel and substrate metallic (Schottky barrier) contact (SBH and bias dependent) 2. Noise generations in Drain is different to those in Source due to ambipolar conduction. UPoN 2008

19. Noise Problems in SBMOS UPoN 2008

20. Summary • Eliminating the limits on the dopant junctions makes SBMOS as one of the most attracting candidates for future CMOS devices, while SBMOS suffers from potential problemson its unique Schottky barrier junctions. • Schottky barrier MOSFETs present particular ambipolar conduction as a function of gate voltage. • Formation of the metallic source/drain using metals silicidation brings about interface states and noise sources. • Unique noises in SBMOS were observed. Proposed noise mechanisms in SBMOS are presented. • Proper noise behavior and mechanisms in SBMOS require further thorough investigations. UPoN 2008