FOcal arrays for Curved Infrared Imagers (FOCII) · • Stress/strain effects on infrared absorber...

DISTRIBUTION A: Approved for public release – distribution unlimited

FOcal arrays for Curved Infrared Imagers (FOCII)

Dr. Whitney MasonProgram Manager

Microsystems Technology Office

FOCII Proposers Day

August 13, 2019

SETA SupportDr. Dick ChengDr. Greg JonesDr. Janet Liu Mr. Robert Faulkner 1


Goals1. Present BAA to community – convey expectations for program2. Q&A for program clarification

• Collect questions (on note cards) • Gov’t team will generate answers during break, poster session, and after meeting• Review answers after the poster session• Publish Q&As in a FAQ attached to the FOCII site under www.darpa.mil/work-

with-us/opportunities3. Poster session – encourage collaboration and team forming

FOCII Proposer’s Day Welcome and Goals

2


FOCII Scope and Objectives

FOCII will produce commercially scalable, large format IR imagers with small ROC3

FOCII will develop and demonstrate:

1) Using no changes to the underlying FPA design process, existing SOA large format (>2k x 2k , ≥55 mm diagonal) cryogenically cooled MWIR and/or LWIR detectors curved to a ROC of 70 mm

2) Using structured arrays, prototype large format (≥2k x 2k with ≥35 mm diagonal) cryogenically cooled MWIR and/or LWIR detectors curved to an extreme ROC of 12.5 mm

DISTRIBUTION A: Approved for public release – distribution unlimited 4

• Evolutionary improvements to the existing state of practice • e.g. small format FPAs (<35 mm diagonal) at large (>70 mm) radius of curvatures (ROC)

• New detector materials• e.g. graphene, transition metal dichalcogenides, colloidal quantum dots, etc.

• Detectors that are not cryogenically cooled or have cutoffs less than 3 microns• e.g. microbolometers, visible, SWIR, or extended SWIR detectors

• Detectors where the integrated detector-ROIC stack is not curved • e.g. compound imagers, fiber bundle imagers

• Trading performance for curvature• e.g. flexible substrates, low fill factors, low QE, low sensitivity, etc.

What FOCII is NOT about

Proposals that principally rely on any of the above will be deemed non-conforming and will not be reviewed


The FOCII program has two technical areas:• TA1: Curving state of the art, large format FPAs• TA2: Curving structured FPAs to extreme ROCs

Proposals and Awards:• Separate proposals required for each TA• Multiple awards anticipated for each TA

Three Program Phases• Phase 1, 12 months: Mechanical Structures• Phase 2, 18 months: Integrated FPAs• Phase 3, 18 months: Imaging Demonstrations

FOCII Program Structure

5


FOCII is an UNCLASSIFED program with Controlled Unclassified Information (CUI)• A CUI guide is published with the BAA

It is expected that FOCII performers will generate controlled unclassified information (CUI) and/or controlled technical information (CTI) as part of their research:• CUI is defined as is information that requires safeguarding or dissemination controls pursuant to and

consistent with applicable law, regulations, and government-wide policies but is not classified under Executive Order 13526 or the Atomic Energy Act, as amended, and all CUI shall be marked and safeguarded in accordance with DoDI 5200.01 Volume 4

• CTI is defined as technical information with military or space application that is subject to controls on its access, use, reproduction, modification, performance, display, release, disclosure, or dissemination

• Contractor information systems shall be subject to the security requirements in National Institute of Standards and Technology (NIST) Special Publication (SP) 800-171 “Protecting Controlled Unclassified Information in Nonfederal Information Systems and Organizations”

• NIST SP 800-171 implementation guidance can be found at: https://nvlpubs.nist.gov/nistpubs/specialpublications/nist.sp.800-171.pdf

FOCII Security

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• Technical Area I: Curving state of the art FPAs • Specific technology and processing methods to achieve low ROCs on continuous, integrated FPAs resulting in

strains beyond I% • Specific processing methods for curving continuous, integrated FPAs tied to an advancement of state-of-the-art

infrared imaging performance • Specific performance of curved continuous FPAs, including metrics and specifications

• Technical Area 2: Curving structured FPAs• Specific technology and methods to mitigate stress and strain in structured FPAs• Specific technology and processing methods to produce seam widths between adjacent segments ofless than 20

microns • Specific processing methods for curving discontinuous, integrated FPAs tied to an advancement of state-of-the-

art infrared imaging performance • Specific performance of curved discontinuous FPAs, including metrics and specifications

Definition of CTI for FOCII

Performers uncertain about whether a given dataset contains CTI should request guidance from DARPA7


Technical Area 1: Curving state of the art FPAs • General technology and methods to curve continuous FPAs • Stress, strain, and other mechanical measurements and modeling, including development of mechanical

models for complex and potentially unstable structures• Stress/strain effects on infrared absorber optoelectronic property measurements and modeling • Algorithms when realized in source code, executable formats, or documented in written reports

Technical Area 2: Curving structured FPAs• General technology and methods to relieve stress in structured (i.e. discontinuous) FPAs • Stress, strain, and other mechanical measurements and modeling, including development of mechanical

models for complex stress mitigations• Stress/strain effects on infrared absorber optoelectronic property measurements and modeling • Algorithms when realized in source code, executable formats, or documented in written reports

What is not CTI in FOCII

ALL PUBLICATIONS resulting from FOCII-funded R&D must go through the formal DARPA DISTAR process for pre-publication review and may have publication restrictions in accordance with the contractual requirements

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9

• FOCII seeks to enable:• Uniform performance across the field of view, even with compact optics• New application spaces by shrinking size, weight, and cost of infrared imaging systems

• TA1: Curving SOA FPAs• Enable ultimate performance optically and electrically

• TA2: Curving structured FPAs• Enable minimal size with exquisite performance for new capabilities

FOCII overview: Curve large format FPAs to small ROCs

FOCII’s key challenge will be mitigating the stresses that result from curving a flat focal plane to small radius of curvatureDISTRIBUTION A: Approved for public release – distribution unlimited

0

0.2

0.4

0.6

0.8

1

0 10 20 30

Half FOV (degrees)

Illumination

% Diffraction Limited

Nor

mal

ized

Sig

nal

Nor

mal

ized

MTF


Motivation: Flat focal plane arrays have poor edge illumination and resolution

Today FOCII

∆r ≫ ∆r’

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30Half FOV (degrees)

Illumination% Diffraction Limited

Performance at edge:Illumination ↆ 72% Resolution ↆ 74%

Performance at edge:Illumination ↆ 8% Resolution ↆ 4%

High performance wide field of view imagers require large arrays and small radius of curvature

Nor

mal

ized

Sig

nal

Nor

mal

ized

MTF

MTF=Modulation Transfer Function

10


Motivation: Flat focal plane arrays require large and heavy optics

Today FOCII

• Complex optics system design to fix aberration• Large size and weight

• Simplified optics system to minimize aberration• Low size and weight

r

d

r∆r

∆r ≫ ∆r’′

• RoC = ∞• Optical length = 136mm• 13 elements• Lens weight = 371g

• RoC = 30mm• Optical length = 30mm• 1 element• Lens weight = 10g

The smallest form factor systems require extreme radius of curvature

r

d

r∆r’’

11

0.0001

0.001

0.01

0.1

20 200 2000


What is FOCII trying to do?

FPA Area (mm2)

Radi

us o

f cur

vatu

re-1

(mm

-1)

4k x

4k

10 µ

m p

itch

2k x

2k

12µm

pitc

h

Military and scientific arraysCommercial arrays

HRL seedlingHRL seedling

CBrite

CEA-LETI

MIT/LL

FOCII TA2

FOCII TA1

Human eye

iPho

ne 4

k x

3k 1

.4µm

pitc

h

Every FPA in the world lives down here

12

FOCII changes the trade space around FOV, illumination, MTF and optical system size

Application space for FOCII

Maximum FOV• Space (LEO

constellations)• IRST applications

Optics Size-1

Minimum Optics Size• Seekers• Rotary wing situational

awareness

Maximum Range• Targeting (Army 3rd

Gen; EOTS)

IR System Performance Cube

FOCII

Increase

Dramatically Decrease

Increase


0.0001

0.001

0.01

0.1

20 200 2000


How curving is achieved today and its limitations?

FPA Area (mm2)

Radi

us o

f cur

vatu

re-1

(mm

-1)

4k x

4k

10 µ

m p

itch

2k x

2k

12µm

pitc

h

Military and scientific arraysCommercial arrays

HRL seedlingHRL seedling

CBrite

CEA-LETI

MIT/LL

FOCII TA2

FOCII TA1

Human eye

iPho

ne 4

k x

3k 1

.4µm

pitc

h

Every FPA in the world lives down here

Objective

Microcameras

14

15

TA 1 —Existing Focal Plane Arrays TA 2 —Structured Focal Plane Arrays

Technical Areas

Curving exquisite FPAs for exquisite performance applications

No modifications to the underlying FPA design process

Extreme radius of curvature for the smallest form factor systems

Modifications to the FPA design process required


FPA Architecture

0

50

100

150

200

250

300

350

400

450

500

0 10 20 30 40 50 60 70

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Challenge 1: Managing silicon strain

HRL 40mm RoCHRL 18mm RoC

Radi

us o

f cur

vatu

re (m

m)

FPA Size (mm)

𝜀𝜀 ≈𝑟𝑟2

𝑅𝑅2

Stress challenges:• Bending (∝ thickness)• Tensile (∝ solid angle) • Compressive (buckling

instabilities)• Thermal cycling

𝑟𝑟 =radius of die𝑅𝑅=radius of curvature

Complex interactions between the different stresses and current strain limit of silicon need to be overcome

ε = 1%

ε = 6%


Typical bulk silicon limit


Challenge 2: Managing absorbing layer strain

Conduction Band

Valence Band

Non-uniform stress results in changes in band structure

1% residual non-uniformity can have a 2x impact on range

Changes in the band structure alter detector performance

0% strain-0.84% strain

InP/InGaAs QWIP

Gusakov, APL 79, (2001), 2508

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• Dark current non-uniformity• Responsivity non-uniformity• Signal-to-noise ratio non-uniformity• Spectral response non-uniformity

Deleterious effects of band structure variation


Parameter Units SoA1 Phase 12 Phase 2 Phase 3Size (Diagonal) mm ≥ 55 ≥ 55 ≥ 55 ≥ 55Radius of curvature mm ∞ 140 140 70# of pixels MP >16 N/A > 4 > 4 Pixel fill factor3 % > 90 > 80 > 80 > 80Operability4,5 % >99 N/A ≥ 90 ≥ 95Waveband µm 3-5 3-5 or 8-12 3-5 or 8-12 3-5 or 8-12Noise Equivalent Temperature Difference mK 25 N/A ≤ 25 ≤ 25

Thermal cycles6 - >1000 N/A 200 1000

Dewar bake - 5 days at 100⸰C N/A 1 day at

100⸰C5 days at

100⸰C

FOCII Metrics: TA1

(1) 4096 x 4096, 10 µm pitch, MWIR (2) Surrogate FPA materials(3) Pixel fill factor defined as the ratio of light-sensitive area of a pixel to total pixel area in an image sensor(4) Relative to flat FPA(5) Operability defined as: 0.5*Rmean<R<1.5*Rmean; NEDT < 4X NEDTmean; no row/column outages; no clusters larger than 5x5;(6) One thermal cycle is defined as 300K to 77K to 300K; FPA must still be operable post cycling

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Parameter Units SoA1 Phase 12 Phase 2 Phase 3Size (Diagonal) mm 35 ≥ 35 ≥ 35 ≥ 35Radius of Curvature mm ∞ ≤12.5 ≤12.5 ≤12.5# of pixels MP >2 N/A > 2 > 2Pixel fill factor3 % > 90 N/A > 80 > 80Operability4,5 % ≥ 99 N/A ≥ 95 ≥ 99Waveband µm 8-10.5 3-5 or 8-12 3-5 or 8-12 3-5 or 8-12Noise Equivalent Temperature Difference mK 25 N/A < 25 < 25

Seam width6 µm 0 10 7 3Spherical deviation7 % 0 6 4 2Thermal cycles8 - >1000 N/A 200 1000

Dewar bake - 5 days at 100⸰C N/A 1 day at

100⸰C5 days at

100⸰C

FOCII Metrics: TA2

(1) 1280 x 1024, 12 µm pitch, LWIR (scaled)(2) Surrogate FPA materials(3) Pixel fill factor defined as the ratio of light-sensitive area of a pixel to total pixel area in an image sensor(4) Relative to flat FPA

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(5) Operability defined as: 0.5*Rmean<R<1.5*Rmean; NEDT < 4X NEDTmean; no row/column outages; no clusters larger than 5x5(6) Seam width defined as the width of the discontinuity between the physical edges of adjacent absorbing regions after curving or integration(7) Spherical deviation defined as max│Ras_built- Rspec│/ Rspec(8) One thermal cycle is defined as 300K to 77K to 300K; FPA must still be operable post cycling


Geometric definitions

Radius of Curvature Seam Width Spherical Deviation

𝑆𝑆𝑆𝑆 =𝑚𝑚𝑚𝑚𝑚𝑚 |𝑅𝑅′ − 𝑅𝑅|

𝑅𝑅

R R’

R R’

R R’

R R’

Center of curvature

(imaginary)

Radius of curvature, R

Imaginary circle completing the curve

R

D

minimum R=D/π

Deliverables


Phase 1 (12 months) Phase 2 (18 months) Phase 3 (18 months)

TA1

• Mechanical and electrical model(s)

• Curvature metrics met, ref. Table 1

• Spectral uniformity meeting specifications of Table 1

• Demonstrate curved hybridized arrays

• Demonstrate operability/ thermal cycle reliability

• Demonstrate curved FPA performance

• Demonstrate operability/ thermal cycle reliability

• Test integrated camera

TA2

• Mechanical and electrical model(s)

• Curvature metrics ref. Table 2• Seam width and deviation from

spherical characterized• FPA preliminary design review


FOCII program plan and schedule

FY20 FY21 FY22 FY23 FY24Phase II: 18 MonthsPh. I: 12 Months Phase III: 18 Months

Mechanical/Performance MeasurementTA1: Existing FPAs

TA2: Structured FPAs

Government IV&V

Kickoff

Camera Demo

Camera Demo

Phase 1 (12 months) —Mechanical structures • Demonstrate curvature metrics• Demonstrate spectral uniformity

Phase 3 (18 months) — Imaging Demonstration• Demonstrate focal array performance • Demonstrate operability/thermal reliability• Test integrated camera

Phase 2 (18 months) —Integrated FPAs• Demonstrate mechanical survivability of

curved hybridized arrays • Demonstrate operability/ thermal cycle

reliability

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Mechanical/Performance Measurement

FPA Performance Measurements

Thermal Cycling


Thermal Cycling


Thermal Cycling


Thermal Cycling

• Demonstrate curvature metrics• Quantify seams • Characterize deviation from spherical

• Demonstrate curved FPA performance with improved seams

• Demonstrate focal array performance • Demonstrate operability/thermal reliability• Test integrated camera

TA1

TA2


• Posting Date (PD): August 9, 2019• Proposers Day: August 13, 2019• Abstract Due Date: September 3, 2019• Abstract Feedback: September 17, 2019• FAQ Submission Deadline: October 4, 2019 • Full Proposal Due Date: October 18, 2019

Important FOCII Dates


• Please submit questions via webex module, or via notecard • If questions arise after industry day, please submit questions to [email protected]

• Answers to most questions will be provided after the poster session• All relevant questions and answers will be published as part of the official FOCII FAQs located

at www.darpa.mil/work-with-us/opportunities under FOCII

Questions

mailto:[email protected]

http://www.darpa.mil/work-with-us/opportunities

www.darpa.milwww.darpa.mil


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