Mercury Cadmium Telluride Imagers - A Patent-Oriented Survey

370 Pages·1997·13.153 MB·English

by  Onshage, Anders C.

HANDBOOK OF SENSORS AND ACTUATORS 5
Mercury Cadmium
Telulride Imagers
A Patent-oriented Survey
Anders C. Onshage
European Patent Office
The Hague, The Netherlands
1997
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Introduction to ,the Series
The arrival of integrated circuits with very good performancdpnce ratios and relatively low-
cost microprocessors and memories has had a profound influence on many areas of technical
endeavour. Also in the measurement and control field, modem electronic circuits were
introduced on a 'large scale leading to very sophisticated systems and novel solutions.
However, in these measurement and control systems, quite often sensors and actuators were
applied that were conceived many decades ago. Consequently, it became necessary to improve
these devices in such a way that their performance/price ratios would approach that of modem
electronic circuits
This demand for new devices initiated worldwide research and development programs in the
field of "sensors and actuators". Many generic sensor technologies were examined, from
which the thin- rind thick-film, glass fiber, metal oxides, polymers, quartz and silicon
technologies are t'he most prominent.
A growing number of publications on this topic started to appear in a wide variety of
scientific journals until, in 1981, the scientific journal Sensors and Actuators was initiated.
Since then, it has become the main journal in this field.
When the development of a scientific field expands, the need for handbooks arises, wherein
the information that appeared earlier in journals and conference proceedings is systematically
and selectively presented. The sensor and actuator field is now in this position. For this
reason, Elsevier Science took the initiative to develop a series of handbooks with the name
"Handbook of Sensors and Actuators" which will contain the most meaningful background
material that is important for the sensor and actuator field. Titles like Fundamentals of
Transducers, Thick Film Sensors, Magnetic Sensors, Micromachining, Piezoelectric Crystal
Sensors, Robot Sensors and Intelligent Sensors will be part of this series.
The series will contain handbooks compiled by only one author, and handbooks written by
many authors, where one or more editors bear the responsibility for bringing together topics
and authors. Great care was given to the selection of these authors and editors. They are all
well known scientists in the field of sensors and actuators and all have impressive
international reputations.
Elsevier Science and I, as Editor of the series, hope that these handbooks will receive a
positive response from the sensor and actuator community and we expect that the series will
be of great use to the many scientists and engineers working in this exciting field.
Simon Middelhoek
vi
Mercury Cadmium Telluride Imagers
Summary
The evolution of imager structures using Mercury Cadmium Telluride (HgCdTe) is described
based on published patents and patent applications. The book is divided into two parts. The
first describes monolithic arrays, with the detector elements and read-out means integrated in
the same semiconductor body. The second part describes hybrid arrays, with the detector
elements and the read-out means formed in separate semiconductor bodies.
The types of monolithic arrays discussed are charge coupled device imagers, ambipolar drift
field imagers, static induction transistor imagers, charge injection device imagers and charge
imaging matrices. The part on hybrid arrays has specific chapters on flip-chip arrangements, Z-
technology arrangements, and arrays with the detector array directly contacting the read-out
chip. The remaining hybrid arrays are separated according to whether the detector elements are
provided with individual read-out leads or not.
The cited documents are presented with an introductory part followed by a descriptive part
which in most cases includes one or more figures. An overview of the subject of this book may
be aquired by reading only the introductory parts in combination with the figures.
A patent number index with information about the patent applicants, inventors, priorities and
patent-families, an inventor index, a company index, and a subject index can be found at the
end of the book.
vii
Preface
This book is an attempt to describe the evolution of mercury cadmium telluride (HgCdTe)
imager structures based on published patents and patent applications. Most of the patent
documents cited in this book originate from the part of the systematic documentation at the
European Patent Ofice (EPO) which corresponds to the International Patent Classification
'.
(IPC) H01L27/14
Focus has been direcced to the structures of the imagers. The steps of manufacturing of the
structures have been included when steps of specific interest have been disclosed. It has been
necessary to exclude documents not explicitly mentioning mercury cadmium telluride to reduce
the material to a manageable size. It should be noted that no verification of the feasibility of a
device or its operation is needed to render it patentable. The analysis of certain Japanese patent
applications have been limited to the published Patent Abstract of Japan.
The patent number, the name of the applicant and the date of publication are indicated for each
document cited in the book. A patent number index, an inventors index, a company index and a
subject index is found at the end of the book.
It is not unusual that a patent application has been filed in several countries referring to a
common first filing i.e. priority. These applications are said to belong to the same patent-
family. In this book English-speaking documents of the patent-families have been selected
provided it has been possible. The patent numbers or patent application numbers of other
documents belonging to the same patent-family as a cited document may be found in the patent
number index at the end of the book.
'
HOIL27/14: Devices consisting of a plurality of semiconductor or other solid-state componentsf ormed in or
on a common substrate, including semiconductor components sensitive to infra-red radiation, light,
electromagnetic radiation of a shorter wavelength, or corpuscular radiation of a shorter wavelength, or
corpuscular radiation and adapted for the conversion of the energy of such radiation into electrical energy or
for the control of electricd energy by such radiation.
viii Mercury Cadmium Telluride Imagers
The book is separated into a first part with monolithic arrays and a second part with hybrid
arrays. Each part comprises five chapters. The documents of each chapter are placed in a
chronological order with the documents with earliest priority placed first. The documents are
separated by a star '*'. Sometimes a document has been placed at a position which is earlier
than that which corresponds to its priority date. This has been done when the document shares
basic features with a document already presented in the chapter. The document then follows
directly after the earlier document and the documents are separated by two stars '* *'.
I would like to express my appreciation to all the people who have assisted me in this work and
especially to S. Behmo and A. Cardon, Directors at the EPO, L.J.L. Fransen, S. Greene, P.
Gori and A. Visentin, Examiners at the EPO.
It is my hope that this monography will serve as a usefil summary of the patents and patent
applications in the field of mercury cadmium telluride imagers.
Rijswijk, 1995
A. C. Onshage
X
Note on Cited Patent Documents
An international two-letter country code is used for published patents and patent applications
i.e.1
AT o Austria
AU o Australia
CA e CaIlada
CN o China
DE w Germany (Federal Republic)
EP @ European Patent Office
ES @ Spain
FR o France
GB o United Kingdom
IL '3 Israel
IT o IdY
JP '3 Japan
NL @ The Netherlands
SE @ Sweden
us
o United States of America
wo o International Bureau of W.I.P.O. (PCT-application)
The country code is followed by a one-letter publication code, i.e.
A o First Publication Level
B o Second Publication Level
E @ Reissue Patent
xi
Introduction
In 1958 it was discovered that mercury cadmium telluride alloys Hgl.,Cd,Te are
semiconductors, with a bandgap which can be varied from approximately -0.3 to 1.6 eV as the
variable composition x goes correspondingly from 0 to 1 [l]. This has opened up the
possibility of designing infrared detectors in mercury cadmium telluride tuned for the 3-5 pm
or the 8-14 pm wavelength atmospheric window. The material has been thoroughly studied
since its appearance and oveniews of its properties have been published [2-41. In figure 1, the
energy bandgaphut-off wavelength is shown versus temperature for various values of x.
4
K
e
6 a
m 8
YI
12
20
Fig. 1
Methods of manufacturing mercury cadmium telluride material have evolved from bulk melt
growth to liquid phase epitaxy (LPE) technology, vapor phase epitaxy (WE) and metal-
organic chemical vapoir deposition (MOCVD) [5-71. These new methods have made it possible
to manufacture large two-dimensional focal plane arrays [8-1 11.
Designing infrared detectors and infrared focal plane arrays is however a demanding task. The
task is not made easier by the fact that thermal background radiation at room temperature is
many orders of magnitude greater in the infrared range than in the visible range.
xii Mercury Cadmium Telluride Imagers
Monolithic arrays, in which read-out means are integrated in the same mercury cadmium
telluride chip as the infrared detectors are presented in part one of this book. The chapters in
this part, chapter 1.1 to 1.5, correspond to the operation of the arrays. The arrays discussed
are charge coupled device imagers [12-141, ambipolar drift field imagers, static induction
transistor imagers, charge injection device imagers [ 12,15,16] and charge imaging matrices
[ 17,181. An example of a charge imaging matnce is shown in figure 2 [ 191.
Fig. 2
Detector elements 24, 26 and 28, arranged in rows and columns, are adiressed through
detector address buses 30, 32 and 34. The columns of detector elements are connected by
transjer gates 36, 38 and 40 to pn-junction read lines 42, 44 and 46 which are connected to
output collectors 48, 50 and 52.
Introduction xiii
A problem with the: monolithic arrays is that the techniques for building metal-oxide-
semiconductor (MOS) devices in silicon cannot be transferred intact to narrow bandgap
materials such as mercury cadmium telluride, mainly due to tunneling and avalanche
breakdown occuring ;at very low voltages. A monolithic array, in which read-out electronics is
integrated in the same mercury cadmium telluride chip as the infrared detectors, is therefore
difficult to achieve.
An alternative approach is to form an hybrid array [20]. The detector array is then formed in a
mercury cadmium tellluride substrate and the readout circuits are formed in a silicon substrate.
The hybrid arrays are presented in part two. Detector arrays having detector elements which
are provided with indlividual read-out leads formed in or on a non-active supporting substrate
are presented in chapter 2.1. The detector elements may however be directly connected to a
read-out chip which i:s bonded to the detector chip. A flip-chip bonding technique using indium
bumps may be used as shown in figure 3 [21].
\
\50
32
Fig. 3
A focal plane array is formed in a mercury cadmium telluride substrate 10. Individual
detector elements are connected to a multiplexer circuit formed in a silicon substrate 30 by
means of indium bumps 20.
These detector arrays, as well as detector arrays for which no connectors at all are disclosed,
are presented in a ch,apter2 .2. Sections for cross-talk preventing measures and passivation and
leakage current preventing measures are comprised in this chapter.
When a silicon read-out chip and a mercury cadmium telluride detector chip are bonded
together by the fip-chip bonding process, the chips are exposed to a mechanical stress which
may lead to damage, especially of the fragile detector chip. Damage may also occur due to
mechanical stress generated when the temperature of the detector array is changed. Due to the
small energy bandgap of mercury cadmium telluride, the detector array is normally cooled to
cryogenic temperatures during operation to reduce thermally generated noise. The temperature
cycles which are generated when the array is cooled from room-temperture to an operational
temperature of for example 77 K create mechanical stress in the array due to the difference in
thermal expansion coefficients between silicon and mercury cadmium telluride. The coefficients
of thermal expansion for silicon and mercury cadmium telluride are 1.2 x 10" m/mK and 3.8-
4.5 x lO"m/mK, respectively. Flip-chip arrangements for mercury cadmium telluride detector