Christopher Bower

Active-matrix OLED display backplanes using transfer-printed microscale integrated circuits

Active-matrix organic light-emitting diode (AMOLED) displays have been fabricated using backplanes with transfer-printed microscale silicon integrated circuits (ICs) in place of conventional thin-film transistors (TFTs). The ICs were fabricated using a commercial semiconductor foundry process, and the wafers were subsequently processed to prepare the ICs for transfer-printing. The microscale integrated circuits were transfer printed onto a glass substrate and interconnected using a single-level, thin-film metallization process. The resulting OLED display exhibited good pixel-to-pixel luminance uniformity, high luminance, excellent controllability, and high switching speed. The transfer-printing process achieved good positional accuracy and high yield.

Printing-based assembly of quadruple-junction four-terminal microscale solar cells and their use in high-efficiency modules

Expenses associated with shipping, installation, land, regulatory compliance and on-going maintenance and operations of utility-scale photovoltaics can be significantly reduced by increasing the power conversion efficiency of solar modules through improved materials, device designs and strategies for light management. Single-junction cells have performance constraints defined by their Shockley-Queisser limits. Multi-junction cells can achieve higher efficiencies, but epitaxial and current matching requirements between the single junctions in the devices hinder progress. Mechanical stacking of independent multi-junction cells circumvents these disadvantages. Here we present a fabrication approach for the realization of mechanically assembled multi-junction cells using materials and techniques compatible with large-scale manufacturing. The strategy involves printing-based stacking of microscale solar cells, sol-gel processes for interlayers with advanced optical, electrical and thermal properties, together with unusual packaging techniques, electrical matching networks, and compact ultrahigh-concentration optics. We demonstrate quadruple-junction, four-terminal solar cells with measured efficiencies of 43.9% at concentrations exceeding 1,000 suns, and modules with efficiencies of 36.5%.

On-chip electron-impact ion source using carbon nanotube field emitters

A lateral on-chip electron-impact ion source utilizing a carbon nanotube field emission electron source was fabricated and characterized. The device consists of a cathode with aligned carbon nanotubes, a control grid, and an ion collector electrode. The electron-impact ionization of He, Ar, and Xe was studied as a function of field emission current and pressure. The ion current was linear with respect to gas pressure from 10−4to10−1Torr. The device can operate as a vacuum ion gauge with a sensitivity of approximately 1Torr−1. Ion currents in excess of 1μA were generated.

High density vertical interconnects for 3-D integration of silicon integrated circuits

This paper describes a technology platform being developed for three-dimensional (3-D) integration of thin stacked silicon integrated circuits (ICs). 3-D integration technology promises to dramatically enhance on-chip signal processing capabilities of a variety of sensor and actuator array devices hybridized with silicon read-out electronics. Currently, advanced 3-D integrated infrared focal plane array detectors are being developed within the DARPA vertically integrated sensor arrays (VISA) program. Here, we describe the 3-D integration process flow and demonstrations developed in the VISA program

60.3: AMOLED Displays using Transfer‐Printed Integrated Circuits

Active-matrix OLED (AMOLED) displays have been fabricated using backplanes with transfer-printed microscale silicon integrated circuits (ICs) in place of conventional thin-film transistors (TFTs). The microscale integrated circuits were transfer printed onto a glass substrate and interconnected using a single-level, thin-film metallization process. The resulting OLED display exhibited good pixel-to-pixel luminance uniformity, high luminance, and excellent control. The transfer-printing process achieved good positional accuracy and high yield.

High Density 3-D Integration Technology for Massively Parallel Signal Processing in Advanced Infrared Focal Plane Array Sensors

The paper describes a platform technology for three-dimensional (3-D) integration of multiple layers of silicon integrated circuits. The technology promises to dramatically enhance on-chip signal processing capabilities of a variety of sensor and actuator devices hybridized with Si electronics. Among these applications are high performance infrared focal plane array detectors

Effects of Assembly Process Parameters on the Structure and Thermal Stability of Sn-Capped Cu Bump Bonds

Non-collapsible Cu-Sn bumps (Cu pillars capped with a thin layer of Sn) have been studied recently as a means to vertically interconnect device layers, achieving 3D integrated circuits. The use of Cu-Sn bump structures is attractive for 3D integration for two primary reasons: 1) the rigid nature of the Cu bump allows for very fine pitch interconnections to be made with less risk of bridging than would exist with collapsible solder bumps, and 2) the joint created when bonding Cu and Cu-Sn bumps remelts at a higher temperature than the formation temperature, which allows for the stacking of multiple layers of devices without disturbing the interconnections achieved in previous bonding events. In order to understand the optimal structure and bonding process for fine pitch Cu-Sn bumps, a study was done to investigate the effects of Sn thickness and bonding pressure on the thickness and chemical composition of the bondline between Cu and Cu-Sn bumps. The thermal stability of the bondline was studied by subjecting bonded test samples to multiple temperature/pressure cycles. The bonding strength was evaluated through die shear tests, and the results were correlated with the parameters of the bump structure and with process parameters.

Verification of the O–Si–N complex in plasma-enhanced chemical vapor deposition silicon oxynitride films

Silicon oxynitride films were deposited using a plasma-enhanced chemical vapor deposition process. The bond configurations of the constituent atoms in the deposited film were analyzed using x-ray photoelectron spectroscopy. Analysis of the Si 2p spectra showed the presence of nonstoichiometric silicon oxide and silicon oxynitride. Analysis of the binding energy shifts induced by Si–O and Si–N bond formation indicated an O–Si–N complex was present in the film matrix. Component balance analysis indicated that second-nearest-neighbor bond interactions were not the cause of these energy shifts and supported the presence of an O–Si–N complex.

Transfer printing: An approach for massively parallel assembly of microscale devices

Transfer printing is a new technique that enables the massively parallel assembly of high performance semiconductor devices onto virtually any substrate material, including glass, plastics, metals or other semiconductors. This semiconductor transfer printing technology relies on the use of an elastomeric molded stamp to selectively pick-up devices from a source wafer and then prints the devices onto the target substrate. The key enabling technique is the ability to tune the adhesion between the elastomeric stamp and the semiconductor devices. The transfer process is massively parallel as the stamps are designed to transfer thousands of discrete devices in a single pick-up and print operation. Studies of the process yield indicate that print yields in excess of 99.9% can be achieved. In addition, experiments show that the chips can be printed with placement accuracy better than +/- 5 mum.

Transfer-Printed Microscale Integrated Circuits for High Performance Display Backplanes

Active-matrix organic light-emitting diode displays have been fabricated using backplanes with transfer-printed microscale silicon integrated circuits (ICs) in place of conventional thin-film transistors. The ICs were fabricated using a commercially available semiconductor foundry process, and the wafers were subsequently processed to prepare the ICs for transfer-printing. The microscale ICs were transfer printed onto glass substrates and interconnected using a single-level, thin-film metallization process. The resulting OLED display exhibited good pixel-to-pixel luminance uniformity, high luminance, excellent controllability and high switching speed. The transfer-printing process achieved good positional accuracy and high yield.