CCD sensors for vertex detector

CCD sensors for vertex detector Mirek Havranek FJFI – CTU 9th March 2009

OVERVIEW • Requirements for vertex detector on e+e- collider • CCD operation principle • My contribution in LCFI

Requirements for vertex detector on e+e-collider • Identification short lived particles containing b and c quark • Track reconstruction with precision better then 5 μm • Polar angle coverage |cosΘ| < 0.96 • Read out or store signal within 50 μs

Requirements for vertex detector on e+e-collider • Radiation hardness not so critical • Operation close to interaction point ( r = 1.5 cm ) • RF insensitive • Low mass ______________________ CMOS (MAPS, DEPFET), CCD (CPCCD, FPCCD)

Existing CCD based vertex detector • SLAC, SLC, SLD, VXD3 - 3 layers, 307 Mpix - 20 μm square pixels, 4000 x 800 pixels/CCD - 1200 electrons per MIP, 8-bit flash ADC - track resolution about 5 μm - |cos Θ| < 0.85 - operation temperature -50 oC - 10% amplitude loss at 15 krad

Charge Coupled Device MOS Capacitor • Formation of potential well • Formation of depletion region • Accumulation of minority carriers • Positive charge in the electrode equals to negative charge trapped in the potential well

Charge Coupled Device • Charge generation • Charge collection • Charge transfer • Charge measurement

Charge Generation Simulated by K. D. Stefanov • Thermal generation • Light absorption • Ionizing particles EE-H . . . . . . . 1.14 eV for optical photons EE-H . . . . . . . 3.65 eV for charged particles

Charge transfer • Transfer mechanisms: - thermal diffusion - fringing fields - electrostatic repulsion (large charge packets) • Typical CTE 0.99999 – 0.999999 Ex: Initial charge = 1620 e- CTI = 0.0001 Number of transfer = 1000 -> 147 electrons lost

Charge transfer • Several approaches is used to readout the charge • Architecture of the CCD depends on the desired data rate T ~ M×N T ~ (M/2)×N T ~ M×N/2 T ~ N

Buried Channel CCD • Separates electrons out of Si – SiO2 boundary • Maximum of potential about 100 nm in depth • High charge transfer efficiency [1]

Charge measurement • Two approaches: - buffer the signal and then amplify outside the CCD - direct connection to the charge amplifier [1]

Amplifier luminescence • Amplifier can irradiate the CCD • MOSFET is source of radiation • Mechanism of light emission: - high Vds (nearly closed transistor) - high velocity of charge carriers - appears in BC, SC MOSFETs [1] [1]

Correlated double sampling [1] [1] • Significant reduction of noise • Reduction of DC offset level

LCFI • Aim of LCFI is sensor and readout development for vertex detector on the future e+e- collider • Vertex detector is based on buried channel Column Parallel CCD working at 50 MHz • Low mass sensors, fast compressed readout, 109 channels

Contribution in LCFI • Testing of readout chip CPR2A • Testing of CCD test structure with charge register ISIS2

CPR2A • CMOS ASIC 0.25 μm 2.5 V • 250 ADC channels • 125 voltage channels, 123 charge channels • 5-bit ADC • CDS • Cluster finding logic • Test registers for stand alone testing

CPR2A - results

ISIS2 • CCD-based sensor with charge register • CMOS technology • Save the charge during bunch train • Readout between bunch trains -> fclk ~ 1 MHz instead of 50 MHz • Several test structures: - comb, snake structures for measuring resistance - short CCDs [2]

IDR IG PG SG OG RG RD OD RSEL M0 OS SS Short CCD • Buried channel CCD • 0.18 μm CMOS process (Jazz Semiconductor)

Reference [1] James R. Janesick: Scientific Charge-Coupled Devices, SPIE PRESS 2001 [2] SPIDER Proposal

THANK YOU FOR ATTENTION FJFI – CTU 9th March 2009

CCD sensors for vertex detector