Mercury Cadmium Telluride Imagers (eBook)

A Patent-oriented Survey

A.C. Onshage (Autor)

eBook Download: PDF

1997 | 1. Auflage
436 Seiten
Elsevier Science (Verlag)
978-0-08-052401-6 (ISBN)

Infos

In two parts, this book describes the evolution of mercury cadmium telluride (HgCdTe) imager structures based upon published patents and patent applications. The first part covers monolithic arrays, and the second part describes hybrid arrays. Each part has 5 chapters, with each document placed in chronological order, with the documents with the earliest priority placed first. Focus has been directed at the steps of manufacturing and structures of imagers.

There is an index at the end of the book containing the patent number, the name of the applicant and the date of publication of each cited document.

This monograph will serve as a useful summary of the patents and patent applications in the field of mercury cadmium telluride imagers.

Inhalt

Cover 1
Contents 9
Introduction 11
Part One: Monolithic Arrays 17
Chapter 1.1 Charge Coupled Device Imagers 19
Chapter 1.2 Ambipolar Drift Field Imagers 37
Chapter 1.3 Static Induction Transistor Imagers 55
Chapter 1.4 Charge Injection Device Imagers 65
Chapter 1.5 Charge Imaging Matrices 87
Part Two: Hybrid Arrays 99
Chapter 2.1 Detector Arrays with Individual Detector Element Read-Out Leads 101
Chapter 2.2 Detector Arrays without Individual Detector Element Read-Out Leads 139
– Cross-Talk Preventing Measures 218
– Passivation and Leakage Current Preventing Measures 269
Chapter 2.3 Flip-Chip Arrangements 285
– Thermal Stress Preventing Measures 305
Chapter 2.4 Z-Technology Arrangements 325
Chapter 2.5 Detector Arrays Directly Contacting the Read-Out Chip 345
– Connections made by Through Hole Technologies 390
Patent Number Index 417
Inventor Index 437
Company Index 449
Subject Index 453

Textauszug

Introduction

In 1958 it was discovered that mercury cadmium telluride alloys Hg1 -xCdxTe 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 [1], This has opened up the possibility of designing infrared detectors in mercury cadmium telluride tuned for the 3-5 μm or the 8-14 μm wavelength atmospheric window. The material has been thoroughly studied since its appearance and overviews of its properties have been published [2-4], In figure 1, the energy bandgap/cut-off wavelength is shown versus temperature for various values of x.

Fig.1

Methods of manufacturing mercury cadmium telluride material have evolved from bulk melt growth to liquid phase epitaxy (LPE) technology, vapor phase epitaxy (VPE) and metal-organic chemical vapor deposition (MOCVD) [5-7]. These new methods have made it possible to manufacture large two-dimensional focal plane arrays [8-11]

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.

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 [12-14], ambipolar drift field imagers, static induction transistor imagers, charge injection device imagers [12, 15, 16] and charge imaging matrices [17, 18], An example of a charge imaging matrice is shown in figure 2 [19].

Fig.2 Detector elements 24, 26 and 28, arranged in rows and columns, are addressed through detector address buses 30, 32 and 34. The columns of detector elements are connected by transfer gates 36, 38 and 40 to pn-junction read lines 42, 44 and 46 which are connected to output collectors 48, 50 and 52.

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 telluride 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 individual 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 is bonded to the detector chip. A flip-chip bonding technique using indium bumps may be used as shown in figure 3 [21].

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 chapter 2.2. 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 flip-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 × 10- 6 m/mK and 3.8–4.5 × 10- 6 m/mK, respectively. Flip-chip arrangements for mercury cadmium telluride detector arrays are presented in chapter 2.3. The chapter comprises a section for thermal stress preventing measures.

A detector array having a more compact structure is formed by using the Z-technology [22-24]. These detector arrays are presented in chapter 2.4. An example of such an array is shown in figure 4 [25].

Fig. 4 A stack of silicon chips 14 are glued together. Each silicon chip comprises an integrated circuit and electrical leads which terminate at a focal plane. The leads contact individual photo-detectors of a detector “mosaic” 28. The array also comprises a back plane wiring 30, insulating boards 32, 34 and 36 and a cooling structure 18.

In another approach to form a detector array a mercury cadmium telluride detector chip is directly contacting or directly glued to a read-out chip. These detector arrays are presented in chapter 2.5. An advantage is that the assembly of mercury cadmium and read-out chip may be processed in a silicon-like fashion. A separate section is provided for detector arrays having through holes formed in the mercury cadmium telluride through which the detector elements are connected to the read-out chip [26]. Such a detector array is shown in figure 5 [27].

Fig. 5 A silicon substrate 1 comprises a read-out circuit with input regions 2 and metal electodes 3. Detector elements 10 are formed in a p-type mercury cadmium telluride body 11 which is glued to the silicon substrate. Each detector element comprises an n-type region 13. Apertures 20 extend through the mercury cadmium telluride body. The n-type regions 13 are electrically connected to the metal electrodes 3 by a metallization layer 23 formed in the apertures.

References:

[1] Lawson WD, Nielsen S, Putley EH, Young AS. Preparation and Properties of HgTe and Mixed Crystals of HgTe-CdTe. J. Phys. Chem. Solids. 1959;9:325–329.

[2] Willardson RK, Beer Albert C. Semiconductors and Semimetals, Volume 18, Mercury Cadmium Telluride”. Academic Press; 1981.

[3] Brice John, Capper Peter. “Properties of Mercury Cadmium Telluride”, INSPEC (The Institution of Electrical Engineers). 1987.

[4] Hansen GL, Schmit JL, Casselman TN. Energy gap versus alloy composition and temperature in Hg1 -xCdxTe”. J. Appl. Phys. October 1982;53(10):7099–7101.

[5] Balcerak R, Gibson JF, Gutierrez WA, Pollard JH. Evolution of a new semiconductor product: mercury cadmium telluride focal plane arrays”. Opt. Eng. March 1987;26(3):191–200.

[6] Edwall DD, Bajaj J, Gertner ER. Material characteristics of metalorganic chemical vapor deposition Hg1 -xCdxTe/GaAs/Si. J. Vac. Sci. Technol. A. March/April 1990;8(2):1045–1048.

[7] European Patent Application: EP-A-0135344, The Secretary of State for Defence, GB, Inventors: S. J. C. Irvine, J. B. Mullin and J. Giess, Published: 27.03.85.

[8] Kruer MR, Scribner DA, Killiany JM. Infrared focal plane array technology development for Navy applications”. Opt. Eng. March 1987;26(3):182–190.

[9] Vural K. Mercury cadmium telluride short- and medium-wavelength infrared staring focal plane arrays”. Opt. Eng. March 1987;26(3):201–208.

[10] Scribner DA, Kruer MR, Killiany JM. Infrared Focal Plane Array Technology”. Proc. IEEE. January 1991;79(1):66–85.

[11] Norton PR. Infrared image sensors”. Opt. Eng. November 1991;30(11):1649–1663.

[12] Chapman RA, Borrello SR, Simmons A, Beck JD, Lewis AJ, Kinch MA, Hynecek J, Roberts CG. Monolithic HgCdTe Charge Transfer Device Infrared Imaging Arrays”. IEEE Trans. Electron Devices. January 1980;ED-27(1):134–145.

[13] Cederberg AA, Borrello SR. HgCdTe CCD Area Arrays for Infrared Imaging in the 3-5 μm Spectral Region”. In: IEDM Tech. Dig. December 1982:149–152.

[14] Koch TL, De Loo JH, Kalisher MH, Phillips JD. Monolithic n-Channel HgCdTe Linear Imaging Arrays”. IEEE Trans. Electron Devices. August 1985;ED-32(8):1592–1598.

[15] Lewis AJ, Chapman RA, Schallenberg E, Simmons A, Roberts CG. Monolithic HgCdTe Charge Injection Devices”. IEDM Tech. Dig. December 1979;571–573.

[16] Wei C-Y, Woodbury HH, Wang S.C.-H. A Novel CID Structure for...

Produkt-Details

• Erscheint lt. Verlag: 18.6.1997
• Sprache: englisch
• Themenwelt: Informatik ► Grafik / Design ► Digitale Bildverarbeitung
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Festkörperphysik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Quantenphysik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-052401-X / 008052401X
• ISBN-13: 978-0-08-052401-6 / 9780080524016