Array Detectors

S W McKnight and C A DiMarzio

Focal Plane Arrays

Imaging Systems

H R Runciman, Thermal Imaging, CRC Press

Scanning vs. Staring Arrays• Scanning Systems

– Point detector or linear array with scanning optics– Less complicated detector– Calibration easier– Scanning system expensive, fragile– Fast detector

• Staring Arrays– Multiple detectors elements to capture pixels of image– Less complicated optics (lighter, smaller, no moving parts)– Longer integration time to increase sensitivity– Need multiplexer for signal read-out

• Charge-Coupled Devices (CCD’s) – Charge transfer and collection– Easier processing, less interconnects

• CMOS– Individually addressed and processed pixels – Less power– No loss in tranfer

N-Channel FET Structure

Channel Length1 to 10 m

B, Body

n+ n+

S, Source G, Gate D, Drain

P-Type Material

SiO2 Insulator20-100m

Channel: 2 to 500 m into page

NMOSMetal-Oxide-Semiconductor

Energy Band Picture of MOSFET(No Bias—Flatband)

z

E

Ef

Metal (Al or Poly-Si)

Oxide (SiO2)

Semiconductor (p-Si)

Ec

Ev

Energy Band Picture of MOSFET(Positive Gate Bias)

z

E

Ef

Metal (Al or Poly-Si)

Oxide (SiO2)

Semiconductor (p-Si)

Ec

Ev

Va

Фb1

Фb2

MOSFET Carrier Reconfiguration (Depletion Bias)

z

E

Ef

Metal (Al or Poly-Si)

Oxide (SiO2)

Semiconductor (p-Si)

Ec

Ev

Va

Фb1

Фb2

Depletion Region

Creation of Depletion Layer and Inversion Channel

• Depletion layer forms within 1μs after bias is applied

• Inversion channel created by thermally generated carriers in ~ 1 s

• For times short compared to 1 s, non-equilibrium situation with depletion region and empty channel.

• Carriers created by optical absorption or external injection can be stored in well for many ms.

Carrier Injection

z

E

Ef

Metal (Al or Poly-Si)

Oxide (SiO2)

Semiconductor (p-Si)

Ec

EvVa>Vt Depletion

Region

Ef

Optical Injection Vo-Vi

Current Injection

Charge-Coupled Device (CCD)

Channel Length1 to 10 m

B

S G D S D

B

~10 m X nRows

Charge Transfer in CCD

J Allison, Electronic Engineering Semiconductors and Devices, McGraw-Hill

Streetman & Banerjee, Solid State Electronic Devices, Prentice-Hall

Focal Plane Arrays

• Monolithic Technology– Detector and read-out CCD on same chip– Parallel processing (lower cost)– Improved ruggedness– Lower performance – Lower yield

• Hybrid Technology– Detector and read-out fabricated separately and bonded– Single-device processing (more expensive)– Thermal mismatch– Choice of material for better performance

• HgCdTe for IR detector• Silicon for CCD

Hybrid Technology

H R Runciman, Thermal Imaging, CRC Press

Hybrid Focal Plane Array

J L Miller, Principles of Infrared Technology, Van Norstrand Reinhold

Array Interconnects

J L Miller, Principles of Infrared Technology, Van Norstrand Reinhold

Platinum-Silicide Schottky Detectors

Streetman & Banerjee, Solid State Electronic Devices, Prentice-Hall

PtSi Si

EB~0.22 eV ↔ λ=5.6 μ

hν

PtSi Array Detectors

• Low quantum efficiency (~1%)

• Mid-Wave IR detection (1-5μ)

• Long integration time (~1/60 s)

• Good sensitivity ~0.05o C

• Compatible with Si technology

Infrared Night Imaging

Sierra Pacific Infrared, Inc.

Infrared Night Imaging (2:15 AM)

Sierra Pacific Infrared, Inc.

Infrared Imaging—Circuit Hot Spot

Sierra Pacific Infrared, Inc.

Infrared Imaging—Water Damage in Ceiling

Sierra Pacific Infrared, Inc.

Infrared Imaging—Tank Fluid Level

Sierra Pacific Infrared, Inc.

Infrared Imaging--- Building Energy Efficiency

Sierra Pacific Infrared, Inc.

Infrared Imaging—Building Energy Efficiency

Sierra Pacific Infrared, Inc.

Infrared Imaging—Biology

Sierra Pacific Infrared, Inc.

Infrared Imaging—Power Line Faults

Sierra Pacific Infrared, Inc.

Infrared Medical Imaging—Patient Recovering from Spinal Surgery

Sierra Pacific Infrared, Inc.