Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 0 Recent results from R&D towards a vertex detector at the international linear collider Sonja Hillert, University of Oxford, on behalf of the LCFI collaboration 2 nd ECFA workshop on Physics and Detectors at the Linear Collider Durham, 1 st September 2004  Introduction  Physics studies  Thin ladder development  Column parallel CCD and readout chip  ISIS based detector  Future plans

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 1 A vertex detector for the future LC Precision measurements require:  good angular coverage (cos  = 0.96)  proximity to IP, large lever arm: 5 layers, radii from 15 mm to 60 mm  minimal layer thickness ( < 0.1% X 0 ) to minimise multiple scattering  mechanically stable, low mass support  low power consumption High hit density near interaction point requires:  small pixel size: 20  m  20  m  fast readout: NLC / GLC: 8ms, use Column-Parallel CCDs (CPCCDs); read between bunch trains TESLA: 50  s for CPCCDs or 125ms for ISIS-based detector

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 2 Physics Studies  aim: investigate benchmark processes to quantify tradeoffs between requirements on detector precision and integrated luminosity  improvement of tools for these studies : track attachment to secondary vertex flavour tagging  examples: study of impact parameter resolution in R  at track perigee (right): increasing material budget has moderate effect, but performance strongly suffers when beam pipe radius is increased from 15 to 25 mm study of vertex charge reconstruction see talk in detector performance session

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 3 Thin-ladder development How can ladders be made as thin and mechanically stable as possible?  currently focussing on semi-supported silicon, thinned to epitaxial layer (> 20  m): silicon glued to substrate, e.g. beryllium, carbon fibre composites, ceramics, foams; difference in expansion coefficient between Si and substrate can give rise to buckling when lowering the temperature  future option: Novel Structures : replace glue pillars; micromechanical engineering profile of silicon along the length of a ladder studied both by FEA and by measurements on physical models (left); plot: comparison of steel (similar to Be) and carbon fibre (CF) substrate at room temperature and ~ - 50 o C:  strong buckling of the steel substrate (blue),  carbon fibre stable at low temperature (red); but: CF less favourable than Be in terms of the material budget  under further investigation

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 4 Column parallel CCD and readout chip core of LCFI R&D: development of sensors and their dedicated readout chip (CPR)  first CCD (CPC1) received April 2003, CPR1 in June 2003 excellent standalone performance of both devices clock amplitudes down to 2 Vpp and clock frequencies up to 25 MHz reached  first assembly of CPC1-CPR1 (start January 2004): in part of CCD every 3 rd channel connected using wire bonds proof of principle of reading CPC with CPR combined test of different types of channels on both devices  connections at 20  m pitch only possible using solder bump bonds since LCWS (April): detailed tests of first bump-bonded assembly (ongoing)

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 5  two phase, pixel size 20 μm  20 μm  400 (V)  750 (H) pixels  two charge transport regions  wire and bump bond connection pads to readout chip and external electronics The first CCD prototype (CPC1) Direct connections and 2-stage source followers 1-stage source followers and direct connections on 20 μm pitch

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 6 Readout Chip CPR1 ASIC for CPC-1 readout  design: RAL Microelectronics Group  voltage amplifiers for 1-stage SF outputs  charge amplifiers for direct outputs  20 μm pitch, 0.25 μm CMOS process  wire- and bump-bondable  scalable and designed to work at 50 MHz Wire/bump bond pads 250(W)  132(L)  5-bit FIFO bit flash ADCs Charge Amplifiers Voltage Amplifiers 6 mm 6.5 mm 250(W)  132(L)  5-bit FIFO bit flash ADCs Charge Amplifiers Voltage Amplifiers

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 7 Wire-bonded CPC1-CPR1 assembly spectrum: X-ray signals generated in CPC1 (1-stage source followers), amplified and digitised in CPR1 (voltage amplifier channels) total noise ~130 electrons, noise from preamplifiers negligible

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 8 Bump-bonded CPC1-CPR1 assembly  bump bonding performed by VTT (Finland)  connecting to CCD channels at effective pitch of 20  m possible by staggering of solder bumps

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 9 Initial tests of bump-bonded assembly  7 assemblies delivered by VTT, first 3 tested : ADCs tested by applying test voltage; CPC1-CPR1 with X-rays from 55 Fe source: 3 chips work fine (  next page), 3 failed because of dicing problems – will be avoided in the future  working CPR1 chips: all ADC channels functional all charge amplifiers functional 20% voltage amplifiers on working CPR1 chips show no signal, under further investigation  next batch of assemblies in production at VTT

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 10 Results from bump-bonded assembly signal in charge channels (above) : 86 mV expected, 70 mV observed  very good agreement Voltage channels (below): gain at centre is ½ the gain at the edge: timing problem?

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 11 ISIS-based detector  TESLA: signals of 1000 e - to be amplified & read; so far envisaged 20 readouts / bunch train  SLC experience: may be impossible due to beam–related RF pickup  started to investigate alternative architecture: variant of Image Sensor with In-situ Storage (ISIS) during 200 ms between bunch trains: transfer of stored signals to local charge sensing circuits in pixel, column-parallel readout at moderate rate, e.g. 1MHz Idea : charge collection on photogate in each pixel: linear CCD with 20 elements, each storing charge collected during 1 time slice, shifted on at 50  s intervals

Sonja Hillert, University of Oxford2 nd ECFA LC workshop, Durham, 1 st September 2004 p. 12 Future plans  ongoing detailed tests of bump bonded assembly of CPC1-CPR1; dedicated CPR1 test board for further study of various CPR1 related issues  design of next generation of CCD and CPR near conclusion  CPC2 to comprise following features: 3 different sizes, including ‘full length’ devices to be tested at frequencies of few MHz high-speed ‘busline-free’ devices (differing from standard devices in metallisation) ISIS test structure for proof of principle: 16x16 cells on an x-y-pitch of 160  m x 40  m  CPR2 characteristics to include: on-chip cluster finding, allowing sparsified readout  Future evaluation will show, which of our two baseline detector designs for the cold machine option – CPCCDs or ISIS – will be better matched to the requirements.  ISIS R&D still in very early stage ~ much room for further ideas broader international collaboration would be welcome