Song-Jae Lee

Dependence of 1/f noise characteristics of NMOSFETs on body bias and temperature in sub-threshold region

Low frequency noise has become one of the major issues for an analog mixed signal and RF (radio frequency) circuits [1]. Previous studies have extensively analyzed drain/gate bias and temperature dependence of 1/f (flicker) noise in a strong inversion region [2, 3], whereas 1/f noise in a sub-threshold region has been investigated very little. The demand for low power consumption has increased due to the development of single battery cell phones. Hence, to reduce the dynamic power consumption of CMOS circuits, threshold voltage must be scaled down without degrading circuit speed or operating logic noise margins. Although Vth scaling is limited by the off-current and static power consumption constraints, a constant substrate biasing technique is used with standard CMOS technology to improve the performance of CMOS circuits. As this technique is used in analog-integrated circuits, such as current mirror and VCO (voltage controlled oscillator), the dependence of 1/f noise characteristics on body bias need to be analyzed. In addition, the noise characteristic of MOSFETs at high temperature is important for analog circuits because the analog circuits are more sensitive to temperature [4, 5]. However, there was little study on the noise characteristics concurrently considering the body bias and temperature. In this study, 1/f noise characteristics of NMOSFET were investigated for various body bias and temperature in a sub-threshold region.

Effect of surface pretreatment in the thermal atomic layer deposition of Al2O3 for passivation of crystal Si solar cells

H2O or NH4OH (5%) precursor pretreatment in the chamber was carried out before the thermal atomic layer deposition (ALD) of an Al2O3 passivation layer on p-type crystal Si. It was found that the density of negative oxide fixed charges significantly increased, the Al–O combination at the interface changed, the Al/O atomic at the interface of Al2O3/Si decreased, and the effective lifetime increased. The pretreated samples with changes in the Al–O structure at the interface, which made the interface more oxygen-rich, were believed to be the reason for the improvement of the field effect passivation in Al2O3 passivated crystal Si solar cell applications.

Analysis of Matching Characteristics of MIM Capacitors with Al 2 O 3 /HfO 2 /Al 2 O 3

In this paper, matching characteristic of MIM (metal-insulator-metal) capacitor with (AHA) structure is analyzed. The floating gate capacitance measurement technique (FGMT) was used for analysis of matching characteristic of the MIM capacitors in depth. It was shown that matching coefficient of AHA MIM capacitor is 0.331% which is appropriate for application to analog/RF integrated circuits. It was also shown that the matching coefficient has a more strong dependence on the width than length of MIM capacitor.

Dependence of the 1/f Noise Characteristics of CMOSFETs on Body Bias in Sub-threshold and Strong Inversion Regions

In this paper, the 1/f noise characteristics of n-channel MOSFET (NMOSFET) and p-channel MOSFET (PMOSFET) are analyzed in depth as a function of body bias. The normalized drain current noise, S ID /I D 2 showed strong dependence on the body bias in the sub-threshold region for both NMOSFET and PMOSFET, and NMOSFET showed stronger dependence than PMOSFET on the body bias. On the contrary, both of NMOSFET and PMOSFET do not exhibit the dependence of S ID /I D 2 on body bias in strong inversion region, although the noise mechanisms of two MOSFETs are different from each other.

Analysis of Device Characteristics of NMOSFETs on Fluorine Implantation

In this paper, we investigated the device performance on fluorine implantation, hot carrier reliability and RTS (random telegraph signal) noise characteristics of NMOSFETs. The capacitance of the fluorine implanted NMOSFET decreased due to the increase of the gate oxide thickness. RTS noise characteristics of the fluorine implated NMOSFET was improved approximately by 46% due to the decrease of trap density at Si/ interface. The improved gate oxide quality also results in the longer hot carrier life time.

Characterization of Al 2 O 3 -HfO 2 -Al 2 O 3 sandwiched MIM capacitor under DC and AC stresses

Metal-insulator-metal (MIM) Capacitors are widely used for radio frequency (RF) and analog mixed signal (AMS) circuits, and dynamic random access memory (DRAM) applications [1]. Although high capacitance density of MIM capacitor for RF and AMS circuits is required to reduce the chip size and system cost, the conventional dielectric materials, such as SiO 2 and Si 3 N 4 , as the thickness of dielectric scales down, emerge as key limitations due to high leakage current and reliability issues. High-k (HK) dielectric, such as HfO 2 , Al 2 O 3 , ZrO 2 , Ta 2 O 5 , and La 2 O 3 , is necessary to achieve the high capacitance density and to reduce the leakage current [2]. Among the various HK dielectric candidates, hafnium-based MIM capacitors are widely used due to their high capacitance density, good thermal stability, and high band gap [3]. However, HK dielectric for MIM capacitors induces high voltage linearity and poor reliability characteristics after electrical stress, due to defects in the metal-insulator interface. The reliability characteristic of MIM capacitor under electrical stress is related to the injected charge in the interface of HK dielectrics [4]. These degradations cause the distortion of MIM capacitors, which limits the performance of the RF and AMS circuits. Hence, an accurate analysis of the degradation of MIM capacitor under electrical stress is required in order to stabilize these characteristics. Moreover, various kinds of voltage shape can be applied to the MIM capacitors. However, there was little study on the effect of stress voltage type on the reliability of advanced MIM capacitors. In this work, reliability of MIM capacitor with high capacitance density was analyzed using three kinds of voltage stress; constant voltage stress (CVS), unipolar voltage and bipolar voltage stresses.

Improvement of thermal stability of Ni-germanide with co-sputtering of nickel and palladium for high performance Ge CMOSFET

As the scaling of silicon (Si) CMOS device continues, new materials such as SiGe, Ge, group III-V semiconductor, CNT, and Graphene are introduced due to the limit of Si CMOS such as short channel effects (SCE) and mobility degradation. Ge metal oxide semiconductor field effect transistors (Ge-MOSFETs) have received a lot of attention because of their higher carrier mobility compared with Si. Other advantages of Ge are its lower melting point and lower thermal budget processes compared with Si. However, Ge technology also has disadvantage. Currently, Ge MOSFET devices face several challenges such as water solubility, poor stability of germanium oxides, and small band gap [1–2]. The smaller band gap of Ge leads to higher off-current in MOSFET due to its higher source/drain junction leakage and worse SCE.

Characterization of Sandwiched MIM Capacitors Under DC and AC Stresses: Al 2 O 3 -HfO 2 -Al 2 O 3 Versus SiO 2 -HfO 2 -SiO 2

In this paper, reliability of the two sandwiched MIM capacitors of (AHA) and (SHS) with hafnium-based dielectrics was analyzed using two kinds of voltage stress; DC and AC voltage stresses. Two MIM capacitors have high capacitance density (8.1 fF/ and 5.2 fF/) over the entire frequency range and low leakage current density of ~1 nA/ at room temperature and 1 V. The charge trapping in the dielectric shows that the relative variation of capacitance () increases and the variation of voltage linearity (/) gradually decreases with stress-time under two types of voltage stress. It is also shown that DC voltage stress induced greater variation of capacitance density and voltage linearity than AC voltage stress.

Comparative Analysis of Flicker Noise and Reliability of NMOSFETs with Plasma Nitrided Oxide and Thermally Nitrided Oxide

In this paper, flicker noise characteristic and channel hot carrier degradation of NMOSFETs with plasma nitrided oixde (PNO) and thermally nitrided oxide (TNO) are analyzed in depth. Compared with NMOSFET with TNO, flicker noise characteristic of NMOSFET with PNO is improved significantly because nitrogen density in PNO near the Si/ interface is less than that in TNO. However, device degradation of NMOSFET with PNO by channel hot carrier stress is greater than that with TNO although PMOSFET with PNO showed greater immunity to NBTI degradation than that with TNO in previous study. Therefore, concurrent investigation of the reliability as well as low frequency noise characteristics of NMOSFET and PMOSFET is required for the development of high performance analog MOSFET technology.

Study on Electro-optic Characteristics and Dynamic Stability Depending on the Pretilt Angle for the Twisted Nematic(TN) and Fringe-field Switching(FFS) Mode

We studied on the electro-optic characteristics and dynamic stability according to an undesirably defined pretilt angle induced in high step coverage of pixel area for the Twisted Nematic (TN) / Fringe-Field Switching (FFS) mode. In case of the TN mode, LC directors twist reversely near the edges of thin-film-transistor and black matrix where the pretilt angle of the LC is not well defined. Therefore, the voltage-dependent dynamics of the LC in TN mode is unstable and shows the bad electro-optic characteristics. On the other hand, in case of the FFS mode, the LCs are twisted parallel to the bottom substrate by fringe electric field and the electro-optic characteristic is not influenced by the pretilt angle of the LC which is not well defined.