R. H. Richter et al - VERTEX 2002 Kailua-Kona, 05.11.2002 DEPFET sensors for a LC vertex detector (1) »DEP(leted)F(ield)E(ffect)T(ransistor) operation

R. H. Richter et al - VERTEX 2002 Kailua-Kona, 05.11.2002

DEPFET sensorsDEPFET sensors for a LC vertex detector (1) for a LC vertex detector (1)

» DEP(leted)F(ield)E(ffect)T(ransistor) operation principles

» Results of pre-tests

» DEPFET prototype run

» Technology, simulation and design

» Wafer thinning

» Concept, first results

» Summary

L. Andriceka, P. Fischerb, K. Heinzingera, P. Lechnera, G. Lutza, I. Pericb, M. Reichec, R.H. Richtera, G. Schallera, M. Schneckea, F. Schoppera, H. Soltaua, L. Strüdera, J. Treisa, M. Trimplb, J. Ulricib, N. Wermesb

aMPI Halbleiterlabor Munich bUniv. of Bonn

cMPI für Mikrostrukturphysik Halle, Germany


DEPFET-PrinzipleDEPFET-Prinziple

FET integrated on high ohmic n-bulk

Collection of electrons within the internal gate

Modulation of the FET current by the signal charge!

p+

p+ n+

n

n+

totally depletedn --substrate

internal gate

rear contact

source top gate drain bulk potential via axistop-gate / rear contact

V

potential m inim umfor electrons

p-channel

p+

Radiation

-

-

- -+

+

++

-

-

~1m

~300 m

Advantages: Amplification of the charge at the position of collection=> no transfer loss

Full bulk sensitivity Non structured thin entrance window (backside) Very low input capacitance => very low noise


2 4 6

0

1000

2000

3000

4000

5000

6000

Escape - Peak

K

K

# Z

ähle

r

Energie [keV]

ENC = 4.8 +/- 0.1 e-

55Fe-spectra @ 300K

Excellent noise values measured on single pixels

BioScope - imaging of tracer-marked bio-medical samples

(P. Klein and W. Neeser)

Noise: ca. 70 ENC @ 300KSlow operation (old technology)Large arrays are impossible(JFET => VP variations)Large cell size


Rectangular DEPFET pixel Rectangular DEPFET pixel detectordetector

MOS transistor instead of JFET

A pixel size of ca. 20 x 20 µm² is achievable using 3µm minimum feature size.


DEPFETDEPFET pixel matrix pixel matrix

- Read filled cells of a row- Clear the internal gates of the row - Read empty cells

Low power consumption

Fast random access to specific array regions


DEPFET TechnologyDEPFET Technology

Double poly / double aluminum process on high ohmic n- substrate

along p-channel perpendicular to channel (with clear)


Self aligning TechnologySelf aligning Technology

Positions of all essential implantations are determined not by masks but by polysilicon layers

shallow channel implantation

- mandatory for rectangular cells (lateral channel definition)

- reduces parameter variations on the wafer


Technology – pre-testsTechnology – pre-tests

Motivation

o Low leakage current <-> new technology

o First MOS transistor parameters for the DEPFET and readout electronics design

o Process know how and design rules

Pre-tests:

Device test: Single poly, single Al, MOS technology on 300µm silicon

+ Numereous deposition, lithography and etching tests


Pretest results: Diode leakage currentsPretest results: Diode leakage currents

Reference diodes Pre-test diodes

IBulk =100pA/cm2 IBulk =100pA/cm2


Linear Linear MOS Transistors (self aligned technolgy)MOS Transistors (self aligned technolgy)

VGS = -4V...-7V @VB=10V

L=5µm L=7µm


Pixel prototype production (6“ wafer)Pixel prototype production (6“ wafer)for XEUS and LC (TESLA)for XEUS and LC (TESLA)

Many test arrays- Circular and linear DEPFETS up to 128 x 128 pixels minimum pixel size about 30 x 30 µm² - variety of special test structures

Aim: Select design options for an optimized array operation (no charge loss, high gain, low noise, good clear operation) On base of these results => production of full size sensors

Production will be finished in spring

purpose

detector format

pixel size

thickness

noise

readout time/ detector

/ row

particle tracking

1.3 x 10 cm² (x 8)

520 x 4000 pixels

(x 8)

2.1 Mpix (x8)

25 µm

50 µm

~ 100 el. ENC

50 µsec20 nsec

imaging spectroscopy

7.68 x 7.68 cm²

1024 x 1024 pixels

1 Mpix

75 µm

300 ... 500 µm

4 el. ENC

1.2 msec2.5 µsec

Active Pixel Sensor (rectangular)

• 2 pixels

30 x 30 µm²

• DEPFET

L = 5 µm

W = 18 µm

reduce the required read out speed by 2doubles the number of read out channels


Potential during collection - 3D Poisson equation (Poseidon)Potential during collection - 3D Poisson equation (Poseidon) (50µm thick Si, N (50µm thick Si, NBB=10=101313cmcm-3-3,V,VBackBack=-20V)=-20V)

Depth 10µmDepth 7µmDepth 4µmDepth 1µm

So

urce

sD

rain

External (internal) Gates

n+

cle

ar

con

tact

s

Cell size 36 x 27 µm²


Hiding the nHiding the n++-clear contacts-clear contacts

Depth 1µm

The positive Clear pulse removes the electrons from the Internal Gate and also pushs the holesout of the deep p cover region. After returning of theclear the deep p remains negatively charges forminga shield for the signal electrons.


Potential distribution during ReadingPotential distribution during Reading

Internal Gate

Drain

Source

Back contact

2D dynamic simulation along the channel

ID adjusted to 100µA (W/L =18µm/5µm)

Vinternal Gate ca. 3V

Localized charge generation simulates a hit

DEPFET simulation – TeSCA (2D, time dependent)

hit response to a generation of 1600 electron-hole pairs

TeSCA (2D, time dependent)Removal of 1600 electrons from the internal gate (VClear=15V)

Simulation of the Clear mechanism

Poseidon (3D Poisson equ.)Includes 3D effects => VClear=20V


Current production statusCurrent production status

Pixel array section – Design with clockable clear gatePixel array section – Design with clockable clear gate

N-side view with two polysilicon layers and contact openings

To do:

- P-side processing

- Metallization

Drain Gate

Clear

Cleargate

Source

1 Pixel cell


Processing thin detectorsProcessing thin detectors- the Idea -- the Idea -


Detector thinning – first resultsDetector thinning – first results

Wafer bonding – MPI f. Festkörperstrukturphysik, HalleWafer grinding – SICO GmbH, JenaAnisotropic etching – CiS gGmbH Erfurt, MPI Halbleiterlabor Munich

Thickness of detector region : 50µmof frame : 350µm

Size: 8cm x 1cm


SummarySummary

o DEPFET is promising detector candidate for future HE and astrophysics experiments. Key features: low noise, full bulk sensitivity, no charge transfer loss, low power consumption, random access within an array

o A new DEPFET technology (2 poly/ 2 aluminum) was developed for large arrays and high speed operation

o A DEPFET Prototype production has been started with DEPFET arrays with

30 x 30 µm² pixel size (TESLA) to 75 x 75 µm² XEUS

- Technology and device simulations are looking encouraging - Technological pre-tests show very good electrical parameters (leakage currents and MOS transistor characteristics)o A concept for merging the DEPFET technology with a thinning technology is

proposed

- thin mechanical detector samples were fabricatedo First wafers will be finished in spring ‘03


Processing thin detectorsProcessing thin detectors- Wafer bonding -- Wafer bonding -

10 “SOI” Wafer prepared by MPI für Microstrukturphysik, Halle

picture from: www.mpi-halle.mpg.deQ.-Y. Tong and U. Gösele “ Semiconductor Wafer Bonding ”

John Wiley & Sons, Inc.

≈1 cm/sec

Documents

R. H. Richter et al - VERTEX 2002 Kailua-Kona, 05.11.2002 DEPFET sensors for a LC vertex detector (1) »DEP(leted)F(ield)E(ffect)T(ransistor) operation