Download HAPS

Hybrid Active Pixel Sensors
and SOI-Inspired Option
M. Baranski, W. Kucewicz, S. Kuta, W. Machowski, H. Niemiec, M. Sapor
University of Mining and Metallurgy, Krakow
K. Domanski, P. Grabiec, M. Grodner, K. Kucharski, B. Jaroszewicz,
J. Marczewski, D. Tomaszewski
Institute of Electron Technology, Warszawa
M. Amati, A. Bulgheroni, M. Caccia
University of Insubria, Como
Presented by Halina Niemiec
Solutions for future linear collider
Vertex Tracker

Hybrid Active Pixel Sensors
with interleaved pixels
 Charge collection and resolution
 New prototype

SOI monolithic detectors
 Technology challenges
 Test structures and readout prototype
Hybrid Active Pixel Sensors
with Interleaved Pixels - Motivation
Vertex Tracker for future linear collider
should provide:
Single point resolution better then 10 m
Limitations of pixel detectors:
Dimensions of readout electronics cell
 Number of readout channels – power
dissipation, readout speed

Possible solution
Hybrid Detectors with Interleaved Pixels
Hybrid Pixel Detector
with Interleaved Pixels
Readout pixel
p+
Interleaved pixel
Polyresistor
readout pitch = n x pixel pitch
Large enough to
house the VLSI
front-end cell
Small enough
for an effective
sampling
n
Charge carriers generated underneath one of the
interleaved pixel cells induce a signal on the
capacitively coupled read-out pixels, leading to a spatial
accuracy improvement by a proper signal interpolation.
HAPS - First Prototype

Fabricated by Institute of
Electron Technology in
Warsaw, Poland

AC coupled, biasing via
polysilicon resistors

36 test structures with 17
different configurations:

implant width: 34 – 100 m

pixel pitch: 50 – 150 m

# of interleaved pixels: 0-3

readout pitches in both
dimensions: 200 and 300 m
Detector Modeling as Capacitive Network
Ci
Cc
Ci
Cb
Cb- backplane
capacitance
Ci - interpixel
capacitance
CC- coupling
capacitance
The expected charge loss depends on the
ratio between the interpixel and backplane
capacitance
Pixel Capacitance Measurements
Measurements with HP
4280 meter @ 1 MHz

3 bias lines were scratched

Capacitance was measured for

each of lines

3 doublets in parallel

1 triplet

Offset in the linear regression for
the capacitance versus the
number of lines - left-over
parasitic contributions after the
cable correction

2 independent measurements
Pixel Capacitance Measurements


Measurements results were compared with
calculated values (OPERA 3D package)
Max charge loss was estimated using time domain
and simply steady-state method
Design Optimization
Time Domain Simulations

Ggnd from 5 to 20 MOhms  Increase of CCE by 26%

Increase of Cip by 50 %
250
1,4
200
1,2
1,0
150
0,8
100
0,6
50
0,4
0
0,2
-50
0,0
0
50
100
Time [ns]
150
200
Pixelpixel
potential
[mV][mV]
potential
Readout
pixel potential
Interleaved
Pixel potential
[mV] [mV]
 Increase of CCE by 23%
Charge Sharing Studies

Structure under test:

60 m implant width

100 m pixel pitch

200 m readout pitch
Laser light spot
Automatic displacement system
p+
n

Tests with infrared diode:

Wavelength: 880 nm (penetration depth in
silicon substrate: 10 m)

Spot size: below 85 m, position controlled
by 2D stage with micrometric accuracy
Test Module
The read-out pixels were
wire bonded to the
readout electronics chip.
The BELLE experiment
amplifiers and readout
chain were used
Charge Sharing Studies
Description of charge collection properties:
 Charge
sharing:
h= PHR/SPHcluster
PHR – pulse height on reference pixel,
PHcluster – cluster pulse height
 Charge
Collection Efficiency CCE
Cluster pulse height normalized to its maximum
value, corresponding to a charge release
underneath an output node
Charge Sharing Studies
CCE
Interleaved
Readout
Max charge loss:
40%
In good agreement with
estimated values for
capacitive network
Charge Sharing Studies – Resolution

h parameterization allows a coordinate reconstruction and
resolution measurement
h function

Average resolution
Resolution vs. spot position
Resolution:
 Interleaved pixels (efficient charge sharing): 3 m
 Readout pixels (min charge sharing): 10 m
Resolution – Conclusion

Binary resolution defined by
implant _ pitch / 12
can be improved by about a factor 4 for a
configuration where the ratio between the charge
carrier cloud r.m.s. and the pixel pitch  0.8

Similar scaling factor can be expected for a
minimum ionizing particle detected by a pixel
sensor with 20 - 25 m pitch as long as S/N100
and the charge loss is  50%
Hybrid Pixel Detector
with Interleaved Pixels – New Prototype

Pixel pitch – 25 m x 25 m and 25 m x 50 m
Better single point resolution
 Lower backplane capacitance


Punch-through mechanism for pixel biasing
Smaller distance between pixels – higher interpixel
capacitance
 High value of biasing resistance
 Elimination of polysilicon resistors from technological
process

New Prototype - Topology
p+ diffusion dots for
punch-trough mechanism
Pixel
Bias grid
Punch-through Mechanism Simulations
Bias
line
Pixel
electrode
ATLAS and ATHENA software (SILVACO)
Hybrid Pixel Detector
with Interleaved Pixels – New Prototype
Detectors were fabricated by
Institute of Electron
Technology, Warsaw
Electrostatic characteristics
measurements and charge
collection studies are planned
on a short time scale
SOI Monolithic Detector – Motivation
Advantages of SOI monolithic detectors:

SOI imager as a monolithic device allows to reduce
total sensor thickness

Performance and radiation tolerance of readout
electronics may benefit from reduction of active silicon
thickness

SOI solution allows to use high resistive detector
substrates
The SOI Imager project is partially financed
by European Commission within 5-th Framework Program
SOI Imager – Main Concept
Detector  handle wafer
 High resistive
300 m thick
Electronics  active layer
 Low resistive


1.5 m thick
Detector: conventional p+-n, DC-coupled
Electronics: preliminary solution – conventional bulk MOS
technology on the thick SOI substrate
SOI Substrate for Monolithic Detectors
SOI detectors require high quality
handle wafer substrate

Popular SOI production methods base on SIMOX
(separation by implantation of oxygen) and WaferBonding (wafer oxidation, bonding and thinning, e.g.
BESOI, Unibond®)

Advantages of Unibond® method over SIMOX from SOI
imager point of view:

Resistivity of handle (for detector) and donor (for
electronics) wafer may be optimized

No silicon inclusions and islands in buried oxide

An order lower dislocation density
SOI Imager – Technology Development
Technology of SOI detectors
– integration of pixel manufacturing technique
with typical CMOS polySi gate technology
Challenges:

Quasi-simultaneous fabrication of circuits at both sides
of the BOX layer

Electrical connection to the pixel junction

Thermal budget of the whole sequence and
technological sequence of high temperature processes

Cross-talk between read-out electronics and detector
SOI Imager – Technology Development
Technological sequence  over 100 processes
SOI Imager – Technology Development
Technology Development
Experiments on SOITEC Wafers
Technological experiment was performed to
validate and adjust the technology

The bulk test structures has been used to
produce SOI transistors on SOITEC wafers

The technology sequence was similar as it is
provided for SOI detectors

The substrate parameters are exactly the
same like for future SOI detectors except low
resistivity of the handle wafers
Technology Development
Experiments on SOITEC Wafers
The CMOS transistors on thin substrate (SOI) have
different doping profiles than the bulk ones.
Parameters of well implantation were changed to get
Vth=0.7+/-0.2V at reasonable VBR ( 19 V)
Technology Development
SOI Test Structures
For complete technology characterization
special SOI test structure was designed

General technological test structures
for parameters extraction,
investigation of device mismatches,
process control, reliability test

Examples of analogue and digital
circuits for comparison simulation
and measurements results

Specific test structures for SOI
detector applications
Technology Development
SOI Test Structures
Dedicated test structures for SOI
detector application:

Module for extraction of pixels p-n
junctions parameters in deep cavities

Reliability test structure: chain of
contact windows for pixel detectors
and metal1 serpentine over deep
detector contact window

Matrices of simple readout channels
with contacts to detectors
Technology Development
SOI Test Structures
Readout circuits with detector contacts on SOI substrate
Preliminary solution
Technology Development
SOI Test Structures
The SOI test
structures will be
fabricated by IET,
Warsaw by the end
of the year
Readout Circuit Development
Prototyping in Commercial Technology
In parallel with technology development work on readout
circuit prototyping is carried on. First prototype was designed
in 0.8 AMS technology
Readout sequence
 Compatible with external
CDS processing
 Detector dead time is
limited to the reset time
of integrating element
 Integration time of every
channel is well defined
Conclusion
Two paths of active pixel detectors development
were presented:

HAPS with interleaved pixels

Prototype detectors have been manufactured

Preliminary charge collection studies have confirmed the
validity of this detector concept


Measurements of second prototype (with 25 m) are planned
on a short time scale
SOI detectors

Concept of detector and technological solutions were
presented

Dedicated test structure and readout prototype were designed
and are expected to be fabricated by the and of the year