Defect-Oriented Degradations in
Recent VLSIs：
Random Telegraph Noise, Bias Temperature
Instability and Total Ionizing Dose

Kazutoshi Kobayashi
Kyoto Institute of Technology
Kyoto, Japankazutoshi.kobayashi@kit.ac.jp

AgendaKobayashi Lab.

Introduction
 RTN: Random Telegraph Noise BTI: Bias Temperature Instability
 TID: Total Ionizing Dose Summary2

Dependability & Serviceability
Kobayashi Lab.



Our daily-life highly depends on embeddedsystems

Transportation
Banking

Big problems when failures happen
50 planes
stopped2 million
affectedDec. 2007
Trouble on a train system

Jan 2013
Trouble on 787 airplane3

Reliability Issues in VLSIs
Error Probability

Kobayashi Lab.

Wear Out (BTI)

Bathtab Curve
Wear outfailure

Infant Mortality
failure電子

Temporal failure
Temporal (SEE)Time
Infant Mortality

Thermal neutronHigh-energy neutron

particles

Alpha particle

LERvoids
Wires or Gates

Nuclear Reaction

4Three Topics Related to Defects
Kobayashi Lab.

Bias-induced Temporal Fluctuation
 RTN– Random Telegraph (Signal) Noise

Stress-induced Aging Degradation
 BTI– Bias Temperature Instability

Radiation-induced Aging Degradation
 TID– Total Ionizing Dose5CMOS Technology Scaling
Kobayashi Lab.

Gate Dielectrics
before 180nm

HCI90 ~ 65nm

HCI

NBTI

SiON40nm

HCI

NBTI PBTIHigh-k32 ~ 14nm

HCI

NBTI PBTISiO2CMOS Technology Scaling

RTN

High-k
HCI: Hot Carrier Injection
NBTI: Negative BTI on PMOSPBTI: Positive BTI on NMOS
RTN: Random Telegraph Noise

Aggressive scaling worsens reliability7

Traps (Defects) in Gate Oxide
Kobayashi Lab.

Poly Si

Oxide Trap/ E’ Center

Interface Trap/ Pb Center
SiO2Si
SiliconHydrogen

OxygenHole8Agenda
Kobayashi Lab.

Introduction
 RTN: Random Telegraph Noise BTI: Bias Temperature Instability
 TID: Total Ionizing Dose Summary

9

Random Telegraph Noise
Kobayashi Lab.

Charged carriers are captured (trapped) oremitted (detrapped) in oxide traps.
 Vth (transistor current) fluctuates temporarily.
e: time to emission , c: time to capture

Serious in CCD (Charge Coupled Device)10

RTN-induced Drain Current Fluctuation
Kobayashi Lab.

Vgs = 0.4 Vc0.7 V

e

0.5 V

0.8 V

0.6 V

1.2 V

Time constant （c, e） of RTN strongly depends on gate bias.

11Process Variations vs RTN in Scaled Devices
Kobayashi Lab.

Cumulative Distribution Function

Long-tailRTN
Small MOSFET

Large MOSFETWID

Normal distribution for PV
Long-tail distribution for RTN

Drain Current Fluctuation (linear)Large MOSFET: WID variation dominates

Small MOSFET: RTN can dominate at some realistic  value

12AgendaKobayashi Lab.

Introduction
 RTN: Random Telegraph Noise BTI: Bias Temperature Instability
 TID: Total Ionizing Dose Summary13

NBTI on PMOS and PBTI on NMOS
Kobayashi Lab.

Aging degradation by continuous stress
PMOS

NMOS

NBTI

PBTI

Negative Bias
VSS
VDD

Stress

VDD

After 65nm process
SiON gate dielectric

Positive Bias
VDD
VSSStressVSS

After 40nm process
Hi-k gate dielectric
14

BTI (Bias Temperature Instability)
Vth (Threshold Voltage)

Kobayashi Lab.

Recoverable
Component
PermanentComponent

15

Two Models of BTI
Kobayashi Lab.

Gate
Drain
Interface Trap
Gate
SourceDrain

SourceOxide Trap

Reaction Diffusion Model [Alam, IEDM03]– Carriers are trapped by dangling bond (interface trap)

Atomistic Trap-based Model [Kaczer, IRPS10]– Carriers are trapped /detrapped in oxide trap (same as RTN)
– RTN:
Carriers repeats capture and emission
16– BTI:
Captured carriers are never emitted

BTI Degradation Models
Kobayashi Lab.

Reaction Diffusion Model

n=1/4: atomic H diffusion
n=1/6: H2 diffusion
Atomistic Trap-based Model

17

Measurement Results
Kobayashi Lab.
AA

A

A

A

OUT
B

B

B

B

B

ENB

NBTI

11stage Ring OscillatorOsc.(24 s)

NBTI stressOsc.

…

NOR w/o NBTI ܸgs=0

NOR w/ NBTI ܸgs<0

VDD 2.0V, Temperature 80℃

Stress measurement by Ring Oscillator (RO)– Frequency degradation follows log(t)?
[R. Kishida et.al. IRPS 2015]18

Fitting by Two Models
Kobayashi Lab.

Average Error




0.53%

௡0.02%

Short-time measurement data matches bothmodels
19Long-term Prediction
Kobayashi Lab.

tn fitting seems to be too pessimistic?





௡

After 108 seconds (3 years), log fitting has a
few % degradation, while tn fitting has 20%
degradation.
20

RTN and BTI
Kobayashi Lab.

[IEDM14, 34-6]

Large device: smooth degradation by many traps.
 Small device: discrete degradation by several traps.
BTI is caused by oxide traps, not by interface traps
21RD Model or Trap-based Model
Kobayashi Lab.

Hot discussions in IRPS
over decades Recently, Trap-basedmodel has moresupporters– How H is diffused back tointerface trap on recovery?
– In RD model recovery depends
on stress/relaxation time only

Recovery on RD model

Measurement data on recovery.
Dots are measurement data.
Lines are predicted by RDmodel.[Grasser, Trans. ED 2011]22

AgendaKobayashi Lab.

Introduction
 RTN: Random Telegraph Noise BTI: Bias Temperature Instability
 TID: Total Ionizing Dose Summary

23

Radiation Effects in Outer Space
Kobayashi Lab.

[RADECS 2015 Short Course]

24

TID (Total Ionizing Dose)
Kobayashi Lab.

Performance degradation on MOS
transistors by protons and electrons– Thicker field oxide is damaged more than thin gate oxide– Leakage path between drain and source by charge in fieldoxide (NMOS only)– Vth shift like BTI (PMOS dominant)[Ratti, Ionizing Radiation Effects inElectronic Devices and Circuits]

25

BTI and TID
Kobayashi Lab.

Both degradations are caused by traps inoxide or interface
 Thicker field oxide is dominant in TID, while
thin gate oxide is dominant in BTI– No bias in field oxide (No BTI)
– Thicker oxide is damaged more than thinner oxide by TID


No confirmed theory is establishedInterface
Trap

Oxide
Trap– Interface traps vs Oxide traps– How hydrogen is related to degradation– Still in debates

26

SummaryKobayashi Lab.

Reliability issues are hot topics in highly-scaled
CMOS circuits Introduce RTN and BTI in terms of defects (traps)
– Oxide traps and interface traps

RTN is temporal fluctuation of Tr. performance BTI is permanent (continuous) degradation of Tr.
performance. When stress is released, relaxation(recover) starts
 TID is also related to defects
– TID is dominant in thicker field oxide– BTI is dominant in thinner gate oxideStill in debates about the correct theory

27

Acknowledgement
Kobayashi Lab.

Our lab. members of long-term degradationgroup– Dr. Yabuuchi, Mr. Kishida, Ms. OshimaProf. Takashi Matsumoto of Univ. of Tokyo VDEC, RCNP, Renesas Electronics,Synopsys, Cadence & Mentor Graphics formeasurement, chip fabrication & EDA tools 28