A Vertically Integrated Module Design for Track Triggers at Super-LHC

The environment expected at future LHC upgrades pose unprecedented challenges for particle detector systems.Although the details of the future path of the experiments is uncertain, it is clear that they must be prepared for very high data rates.

1033

1035

1032 cm-2 s-1

1034

Proposal Information

• Proposals are for “generic” R&D, essentially defined as post-phase 1 for LHC• Funding for all proposals is $3M for FY11• $625k each taken from CMS, ATLAS this year -> $1.25M next year• Letters of intent (not mandatory) due mid-Feb, full proposals due March 19• Both CMS and ATLAS have decided to submit a single proposal each – with

details in the appendices – track trigger will be a high priority piece of the CMS proposal

• Funding will be supplemented by FNAL generic R&D funds as well as international collaborators

• We have now heard that some CMS/ATLAS bridge funding should be available for phase 2 projects.

Physics Reach

• Much of the discussion has been aimed at retaining trigger capabilities at sLHC, but we need more than that. This work is intended for an era when the LHC has presumably discovered new physics and the experiments will need to make precise measurements of supersymmetric states, Higgs, KK modes, black holes …

• Much of the new physics is expect to couple to heavy states, b, t – tracking is crucial.

• The new physics could be very complex – supersymmetric states with cascade decays, missing energy … we will need more powerful tools at the trigger level

We need to think about qualitatively new capabilities, exemplified by a L1 tracking triggerThis is not an immodest proposal – we are trying to transform the way trackers and triggering systems are integrated

Tracking Triggers

• Current tools are limited– calorimeter triggers cannot select individual primary vertices, have poor

hadronic energy resolution, depend on isolation– Muon triggers limit the physics reach, especially for complex, multi-object

topologies.• A track-based trigger can provide transformational capabilities

– Selection of a parent primary vertex (z resolution)– Excellent momentum resolution – providing an initial particle flow basis for

triggering– Ability to provide isolation cuts– Excellent matching to calorimeter and muon objects– Access to detailed event topology information.

• It has been done in drift chambers (CDF) and fibers (D0) – can it be done in silicon with much higher granuarity (10x) and event rates (12x)

The Trigger Problem

CMS upgrade “strawman” design: >150 m2 of silicon, >50 M pixel channels, 86 M “strip” channels. Raw hit data (20bits/hit) rate at 40 Mhz crossings, 200 interactions/crossing, 14 TeV• 2.75x1013 bits/second of hits in the tracker – we want to use this

information to make a decision on whether an event is “interesting”• Equivalent to 2x the 2009 US internet bandwidth• Can only record ~1x105/40x106 events/sec ~1/400 crossings• 3.2 ms

decisiontime

340

500

1040

1.7

2.5

Track Triggering

We are interested in triggering on high transverse momentum (stiff) tracks• These have least curvature in the 4T

CMS magnetic field.Filter out and cluster data from low Pt tracks-reduce data by >20

• Curvature information can be analyzed locally – minimal data transfer and associated power– Stacked layers ~ 1mm apart– Local processing and local hit correlation

The 3D Solution

The vertical interconnection ability available in 3D seems to be an optimal solution to this problem• A single chip on the bottom tier can

connect to both top and bottom sensors – locally correlate information

• Analog information from the top sensor is passed to ROIC through theinterposer

• One layer of chips• No “horizontal” data transfer necessary – lower noise and power• Fine Z information is not necessary on the top sensor – long (~1 cm

vs ~1-2 mm) strips can be used to minimize via density in the interposer

Double Stack Concept

8Ronald Lipton, SLAC Inst. Seminar 1/13/20108

Spreadsheet estimate

Data flow:• Hit information flows from top to bottom tier•Bottom (master) tier looks for local correlations, filters clusters, and sends data off-module• Stubs are sent off the rod to a processor which forms local tracks (tracklets) and tracks.

?

Thrusts

1. The development and demonstration of techniques to fabricate robust vertically integrated assemblies of sensors and readout chips.

2. The development very high speed, fault tolerant, designs and associated ICs for transmitting sparse data on a readout module.

3. Mechanical design of a module and it’s associated support. 4. Development of a low mass bump bonded interposer

which must carry all of the module electrical signals, space the sensors by ~1mm, and carry the analog signals

5. Development of processes and techniques to produce large area, fully sensitive, sensor/ROIC arrays with minimal dead area, high yield and low cost.

Ingredients

• Vertical interconnection of top and bottom sensors through ROIC– Provided by TSVs and thinning (also possible with SOI, MAPS)– Tezzaron/Chartered run

• Low mass interposer– Silicon or PCB based technology, etched voids, sensors need to

be separated by ~1-2 mm• Robust, fine pitch sensor-detector interconnection which can

expose the topside TSVs– Direct Oxide Bonding (DBI) by Ziptronix

• Cu-Cu bonding by Tezzaron• SOI-based sensors

• High speed, low power data communication using micropipelines• Low cost, industrial scale fabrication (150 m2)

11 11

Readout IC wafer with TSV from foundry

Sensor

DBI bond

Oxide bond diced ROIC to sensor Wafer.

Flip, thin to expose TSV

Sensor

Contact lithography providesAccess to topside pads for vertical data path Sensor

Thin to expose TSV Interposer

Test, assemble module with interposer

Sensor

BumpBondmodule

Sensor

3D Doublet Layer Construction

Oxide Bonding

• Ziptronix Direct Bonded Interconnect (DBI) based on formation of oxide bonds between activated SiO2 surfaces with integrated metal– Silicon oxide/oxide inital bond at room

temp. (strengthens with 350 deg cure)– Replaces bump bonding– Chip to wafer or wafer to wafer process– Creates a solid piece of material that

allows bonded wafers to be aggressively thinned

– ROICs can be placed onto sensor wafers with 10 µm gaps - full coverage detector planes

– ROICs can be placed with automated pick and place machines before thermal processing - much simpler than the thermal cycle needed by solder bumps

• Initial studies at Fermilab using BTeV ROICS

Wafer Bonding/Tiling Will be used for bonding Tezzaron 3D ICs to sensors• Discussed in detail with Ziptronix

VICTR Chip

• Intended to demonstrate the ingredients of of a 3D-based track trigger– 3D chip with TSVs– Silicon and kapton-based

interposers– DBI oxide bonding and

thinning– Bump bonded assembly– Simple top-bottom tier direct

coincidence

Short Strip TierLong Strip Tier

Front end from ATLAS 3D FEI4

Demonstration Module

Long strip (5mm) sensor

Short strip (1mm) sensor

Interposer

Short stripDBI bonds

Bond pad redistribution

ROIC

.5 mm8 mm

Current Status

• 2D wafers completed – being bonded together to 3D wafers• 2D test wafer (short strip tier) being tested now• First set of sensors complete

– Planarity tested at Ziptronix– Sensors available for bond and quality tests

• Second set complete to last metal– Last metal changes to reflect Ziptronix requests for bond topology

layout changes being completed• Silicon interposers produced – some problems with continuity • Full sized PCB interposer produced – initial lot had poor yield. Second

lot underway.– Use to develop full module design and fabrication

• Readout electronics concept defined– Plan to validate design concepts through 1) simulation and 2) test

chips

Phase II In-chip Logic

• 3D design allows for local logic • Each strip looks at ~ 4 neighbors

– Kill all hits if cluster is too large

– Central strip outputs hit information to internal logic

– Interpolation to ½ strip• External settings for dead or

noisy strips, shift of information in phi, pt threshold

• Neighbor chip sends cluster information for last short strips

• Pipelined design:1. Signal amplification/discrimination2. Local cluster finding3. Global cluster finding4. Pt and charge outputs5. Z clustering?

Full 10 x 10 cm Module

design

CF skin for module protectionand mounting points Sensor

Sensor with integratedROIC

Rigid/flex PC board

Twisted wire interconnect

Low mass spacerBump bonds

Passive components

PCB- based Interposer

Data bus (2 layers)

Data bus (2 layers)

Analog via array600 micron pitch

Neighbor bum

ps

Additional R&D

• Interposer– Kapton/Kevlar-based with material removed– Group through vias to allow for voids– Etching, mechanical drilling to remove material– Planarity, bump bonding of large areas (600-800 micron pitch)

• ROIC– Add functionality – trigger and readout– Understand yield issues with larger area chips– VHDL/Verilog simulation of readout/logic with GEANT input

• Sensor integration/DBI– DBI has tight planarity requirements – special sensor processing with

thin oxide, metal– Can we post process standard sensors to add tungsten plugs and CMP– DBI yield, real costs – see later

Sensor post Processing

• DBI requires flat initial topography for good yield

• BNL sensors specially fabricated• Examine using post processing with

oxide deposition, tungsten sputtering, and CMP to provide wafers with acceptable topography

Yields and Large Area Arrays

• We are trying to build large area arrays of chips (10x10 cm) with low cost, good yield. This is the hardest part of the problem. IC Die are limited to ~2x2 cm reticules– Use known good die – implies die-to-

wafer bonding. – But die-to-wafer is more costly and

suffers from it’s own yield issues– Wafer-to-wafer is cheaper and should

have better overall yield – but there are too many edges (lose 3x thickness for guard ring)

• Is there a way to combine both?

Die-based Assemblies

• Technology has been demonstrated (VTT, MIT-LL (FNAL), … to build edgeless sensors with DRIE (3D sensor) technology

• The VTT process, which involves first bonding the sensor to a handle wafer is well adapted to wafer-to-wafer oxide bonding

Edgeless chip-sensor assemblies

5-Year Plan

VICTR Chip

Sensor design and fab

IC/Sensor bonding

Interposer

Bump bond and test

Mechanical Studies

VICTR 2

Multi chip modules

Architecture and simulation

Chip prototypes for high speed transmission

FY2011