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DISTRIBUTION STATEMENT D. Distribution authorized to DoD and their DOD contractors only.Other requests shall be referred to AFRL/CCX, 1864 4th Street , Wright-Patterson AFB, OH 45433-7132

Progress in measuring and modeling NBTI in nitrided SiO2 gate MOSFETs

Kenneth E. KambourSAIC On-site Research Contractor

Electronics Foundations Research GroupSpace Electronics Branch

Space Vehicles Directorate

2

Collaborators

EXPERIMENT

Duc Nguyen, 3rd year student UNM/AFRL RVSE

Camron Kouhestani, 3rd year student UNM/AFRL RVSE

Rod Devine, Think Strategically/AFRL RVSE

THEORY

Ken Kambour, SAIC/AFRL RVSE

Harry Hjalmarson, Sandia National Labs.

TECHNOLOGIES

130 nm IBM Bulk – nitrided SiO2

90 nm IBM Bulk – nitrided SiO2

45 nm IBM SOI – nitrided SiO2

32 nm TI – HfSiON Bulk

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NBTI Experiment

Type I Gate dielectrics – SiO2, lightly nitrided SiO2

Room temperature NBTI due to interface state generation DVth = A t a

0.16 ≤ a ≤ 0.25

Type II Gate dielectrics- nitrided SiO2, HfSiON

Room temperature NBTI due to interface state generation and hole

tunneling from the inversion layer into neutral traps in the near interface

region. Oxide traps charge quickly but also relax quickly if bias is

removed/reduced.

Need to measure NBTI dynamically to capture full effect of charging

44

Example of room temperature NBTI in 130 nm channel length devices with3.2 nm nitrided SiO2 gate dielectric.

Comparative Stress and Recovery Data for 130 nm at Room Temp.

10-5 10-4 10-3 10-2 10-1 100 101 102 103

-0.07

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01 Sweep Trial 1 Sweep Trial 2 Single Point Single Point trial #2 Sweep Method of multiple steep slope points

Thre

shol

d V

olta

ge S

hift

(V)

Accumulated Stress Time (seconds)

Stressing (Vgs = -3.3 V) Recovery (Vgs = 0 V)

10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103-0.08

-0.07

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

Thre

shol

d V

olta

ge S

hift

(V)

Accumulated Recovery Time (seconds)

5

Evolution of NBTI Study (Experiment)

Stress

Short time regime (tstress < 1 sec)

Model DVth(t) assuming full field dependent tunneling

only oxide trapped charge relevant

Long time regime (tstress > 100 sec)

Model DVth(t) assuming oxide trapped charge saturated

only interface state term evolves.

Recovery

Model short time regime as de-trapping via tunneling

Model of long time interfacial trap relaxation (exists)

Develop an NBTI model enabling prediction of frequency and duty

cycle dependence

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Circuit Response - Cao's approach

Uses the Alam model for NBTI to determine the ΔVth as a function of duty cycle and age .(only interface states)

Determines the effect of changing the PMOS threshold voltage, the capacitive load, and the input slew rate on the delay time of a CMOS NAND gate composed of PMOS and NMOS devices.

Once this is done, treats the NAND gates as single devices rather than combinations of MOSFETs.

Apply to multiple standard digital logic (benchmark)circuits used to test the timing. (ISCAS ’89)

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RVSE Approach

Develop our own formula, either theoretical or empirical, for ΔVth as a function of duty cycle and age.

Recreate Cao's basic results.

Currently using Predictive Technology Model (PTM) SPICE device models for 65 nm MOSFETS.

PTM (ptm.asu.edu) is a standard set of device libraries. Channel lengths from 180 nm down to 22 nm.

Ultimately implement modeling software capable of treating much larger scale circuits

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Xyce

Xyce was developed at Sandia National Labs.

Why choose Xyce? Designed for large scale problems. (23,000,000 devices have been

simulated) Potential access to source code. Can model both digital devices (NAND, NOR, AND, & OR gates) and

transistors. Access to local expertise. Xyce has radiation modeling developed which we could obtain in the

future if we wish.

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CMOS NOR and NAND Gates

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Effect of DVth on td

As the threshold voltage changes, for example due to NBTI, the delay time rises for both NOR (green) and NAND (yellow) gates.

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Effect of ti on Delay and to

As the input slew rate rises, for example if one input for the NAND gate is the output of a prior NAND gate experiencing a Vth shift, the delay (blue points) and output slew rate (red points) rises.

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C17 Benchmark Circuit

C432 Benchmark Circuit 233 logic gates including other gates made by sets of NANDS

752 PMOS and 752 NMOS devices

Working in Xyce

Simulation of transient switching of one input takes 3 seconds.

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Ring Oscillator

• Implemented a ring oscillator to determine the effect of ΔVth on frequency

• 11 NAND gates using the 65 nm PTM models

• If ΔVth=0.1 volts, the frequency changed by 15%

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Conclusions

Experiment

The dynamic measurement system works well

We are close to being able to model the complete

short time long time behavior of NBTI

Need access to a much larger reservoir of devices

ideally with controlled process variations

Theory

Modeling of the effects of NBTI on limited circuit size

examples is operative

Implementing the modeling in Xyce to predict response

of much more complex circuits