The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Fully 2D Tileable Photodiode Detector for Medical Computed Tomography Imaging

Fan Ji

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Electronics, Communications and Automation for public examination and debate in Large Seminar Hall of Micronova at Helsinki University of Technology (Espoo, Finland) on the 6th of November, 2009, at 12 noon.

Overview in PDF format (ISBN 978-952-248-119-1)   [8049 KB]
Dissertation is also available in print (ISBN 978-952-248-118-4)

Abstract

This thesis presents a novel design of 2D tileable photodiode detector for medical CT imaging application. The novel design integrates the through-wafer interconnect (TWI) technology into the conventional photodiode structure to achieve 2D tileable capability. With respect to the TWI technology, a new development of the upside down "T" shape TWI is reported for the first time in this thesis comparing to the existing straight TWI, and it shows better electrical properties and allows more robust processing capability. This thesis describes two structures of the photodiode integration with the TWI: via-outside-pixel (VOP) and the via-inside-pixel (VIP). The VIP structure shows advantages over the VOP structure with compact photodiode pixel arrangement. Moreover, it allows sophisticated guard ring protections to further improve the photodiode characteristics. This thesis reports experimental and theoretical studies on the effect of two different guard ring designs to the photodiode application. Upon the design and the fabrication of the novel photodiode chip, the properties of the photodiode are characterized in three aspects (electrical, optical and thermal properties) in this thesis. All the measurement and simulation data show that the demonstrated photodiode samples with the novel design can either meet or exceed the requirements (better image resolution, faster scanning speed and higher coverage rate) of the modern CT detector.

This thesis consists of an overview and of the following 6 publications:

  1. Fan Ji, Seppo Leppävuori, Ismo Luusua, Kimmo Henttinen, Simo Eränen, Iiro Hietanen, and Mikko Juntunen. 2008. Fabrication of silicon based through-wafer interconnects for advanced chip scale packaging. Sensors and Actuators A: Physical, volume 142, number 1, pages 405-412. © 2007 Elsevier Science. By permission.
  2. Fan Ji, Mikko Juntunen, Iiro Hietanen, and Simo Eränen. 2007. Advanced photodiode detector for medical CT imaging: Design and performance. In: Proceedings of the 2007 IEEE International Symposium on Industrial Electronics (ISIE 2007). Vigo, Spain. 4-7 June 2007, pages 2730-2735. © 2007 IEEE. By permission.
  3. Mikko Juntunen, Fan Ji, Kimmo Henttinen, Ismo Luusua, Iiro Hietanen, and Simo Eränen. 2007. Fully tileable photodiode matrix for medical imaging by using through-wafer interconnects. Nuclear Instruments and Methods in Physics Research A, volume 580, number 2, pages 1000-1003. © 2007 Elsevier Science. By permission.
  4. Fan Ji, Juha Kalliopuska, Simo Eränen, Mikko Juntunen, Iiro Hietanen, and Seppo Leppävuori. 2008. Via-in-pixel design of truly 2D extendable photodiode detector for medical CT imaging. Sensors and Actuators A: Physical, volumes 145-146, pages 59-65. © 2007 Elsevier Science. By permission.
  5. Fan Ji, Mikko Juntunen, and Iiro Hietanen. 2009. Electrical crosstalk in front-illuminated photodiode array with different guard ring designs for medical CT applications. Nuclear Instruments and Methods in Physics Research A, volume 607, number 1, pages 150-153. © 2009 Elsevier Science. By permission.
  6. Fan Ji, Mikko Juntunen, and Iiro Hietanen. 2009. Evaluation of electrical crosstalk in high-density photodiode arrays for X-ray imaging applications. Nuclear Instruments and Methods in Physics Research A, volume 610, number 1, pages 28-30. © 2009 Elsevier Science. By permission.

Keywords: through-wafer interconnect, tileable photodiode, guard ring, computed tomography, silicon

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© 2009 Helsinki University of Technology

Last update 2011-05-26