Why study SOI MOSFETs nonlinearities ? Distortion Silicon-on-Insulator (SOI) MOSFET SOI  Simplified process Low parasitic capacitances Low leakage current Low Vth => promising for RF ICs f Non-idealities of “linear circuits” Amplifiers Active filters Used in some applications Mixers Oscillators Frequency multipliers Inherent to the physics of semiconductors ghj

FD vs PD SOI MOSFETs ID [mA] - : Fully Depleted (FD) G S/D Burried Ox ID [mA] - : Fully Depleted (FD) G Burried Ox S/D body --: Partially Depleted (PD) with floating body VD [V] DuTs: FD and PD SOI MOSFETs, 12x6.6 µm/0.25 µm (0.25 µm LETI technology)

What happens inside? - gd kink - High E field near the drain: Impact Ionization current + => impact ionization => creates e--h+pairs + => injection of holes inside the body => body potential increase up to Vtsb => Parallel path for Id and Id increase => Vt lowering and Id increase n ++ p n ++ Body region Depletion region SiO2

The simplest is the best Linearity of SOI MOSFETs using Integral Function Method and Volterra modeling => Does the kink influence the linearity ? => Which methods to characterize the linearity of MOSFETs ?? The simplest is the best DC based characterization methods Taylor series Integral Function Method (IFM) Comparison with Large-Signal Network Analyzer (LSNA) measurements HF MOSFET model based on Volterra series Frequency limitation of DC based methods Third order intermodulation Conclusions Devices performances Outline

Method : Taylor analysis Consider the memoryless nonlinear system: VG(t) ID(t) VG ID t f t f If the circuit is excited by a sine wave, Taylor series:

Methods: quid for large amplitude? VG Taylor: add terms => too complicated ! IFM: good approximation of HD at LF further advantage: less sensitive too measurement noise [CerdeiraSSE02, CerdeiraSSE04, CerdeiraICSICT04]

[CerdeiraSSE02, CerdeiraICSICT04] IFM: How does it work ? 2. Observe that Area1-Area2 is proportionnal to the THD 3. Define the D function Area2 Area1 1. Normalize the characteristics Out In HD3 is obtained by computing the D function of Ir = I(V)-I(-V) => even harmonics eliminated ! HD of order higher than 3 are neglected [CerdeiraSSE02, CerdeiraICSICT04]

IFM takes the influence of the amplitude of the applied signal into account HD3 [dB] VG [V] Not by a scale factor as from Taylor approach, cfr.

Comparison with LSNA measurements full-wave (magnitude and phase) RF (900 MHz) characterization (V,I fundamental and harmonics at input and output) in single take => Real RF nonlinear behavior [VerspechtMTTS95] 900 MHz, 50 Ω, A = 0.2 V Good agreement before the minimum Minimum located at : - IFM : max. of gm - LSNA : max. of power gain Nonlinearity of gm and gd LSNA HD2 [dB] gm and gd gm only VG [V]

Harmonic distortion af HF DC method vs 900 MHz measurements in agreements => Which frequency limit ?? => Answer this question with the help of a Volterra series based model: RG Cgd Cgs Gm Gd Cds YL Vin Gm=gm1+gm2VG+gm3VG² Gd=gd1+gd2VD+gd3VD²

HD from Nonlinear current method freq fp fz [ParvaisGAAS04]

Poles of HD2 and HD3 as a function of ZL Pole Voltage Gain Av 26 GHz 9 GHz 5 GHz Pole HD2 Pole HD3

Characterization methods Good agreements between results calculated using IFM and using Fourier coefficients. IFM: advantages = amplitude dependent, no derivatives. Frequency validity range cfr. Volterra model (several GHz).

HD: PD ~ FD transistors

Frequency analysis of the kink effect frequency limitation caused by RC body impedance iii Vb Rb Cb [SinitskyIEDL97] As Vd  Rb  => fc  Rb and Cb= body resistance and capacitance

Third order intermodulation Volterra model: ZL↑ Kink effect !

PD SOI: Floating body or not ? PD, from ST Microelectronics 60x 1µm/0.12 µm, f=2 GHz FB: higher fT, fmax than BC and isoc. BC/Isoc.: parasitic C, gm degradation

Conclusions At 900 MHz, when the polarization voltage is varied, HD is dominated by the DC I-V characteristics. Frequency validity range of DC methods provided by a Volterra model. PD versus FD: HD ---> idem (gm dominates) IMD ---> depends on the tone separation cfr. Kink effect Thanks to FRIA for financial support