High Density Interconnects for the HL-LHC

This proposal addresses a pressing need in the detector development community within experimental high energy physics (HEP). The HEP community has been involved in the development of highly segmented and miniaturized detection elements ever since silicon strip detectors were first invented in the late 1970s. Various experiments have employed silicon detectors in a variety of readout configurations, such as silicon drift detectors, charge-coupled devices, hybrid pixel detectors, silicon-based calorimeters, and even trackers in satellites. The high luminosity LHC (HL-LHC) has raised a new challenge for the technology: the future of HEP lies in development of increasingly complex detectors with resident intelligence, e.g., trackers with Level-1 trigger, pixel detectors with even finer segmentation, and calorimeters involving a massive increase in scale. Furthermore, these detectors will all need to be hardened against the unprecedented levels of radiation dosage expected at the HL-LHC. Continued expansion in scale, density, complexity, and radiation hardness of silicon-based detectors requires concurrent development of technologies that enable interconnections between detector elements, readout electronics and data acquisition systems. In some sense, the interconnection capabilities are partly driving the innovations in detector design and inspiring bold triggering concepts. Moreover, these designs require layers of novel materials whose thermal, mechanical and radiation tolerance properties need to be studied independently and also within assemblies that include the interfaces. Advance Research Corp. (ARC) has been a leader in the development of technologies involved in hybridization, the process which provides interconnection between sensors and corresponding readout integrated circuits (ROICs). They offer a multitude of solutions aimed at particular problems requiring hybridization. Prof. Tripathi at UC Davis has been involved with silicon detectors since the early 1980s and has worked on several HEP detectors, especially in the areas of readout electronics and detector fabrication using interconnect techniques. Prof. Thom at Cornell is an expert in the technical needs of the CMS tracker in the HL-LHC era, and is emerging as a leader in the management structure of the pixel project. A major strength of our team is the perfect combination of engineering provided by ARC and the expertise in HEP detectors brought by the academic faculty. The issue present in the HL-LHC and other HEP experiments, is not the bump size and pitch, but rather the issue of Dielectric Breakdown. During operation, due to radiation damage, the ROIC chip needs to supply the sensor with upwards of 500-600V. The issue, is that at these potential differences, the ROIC will short to the sensor. In order to prevent shorting, the interconnects need to be surrounded by a dielectric with sufficient breakdown strength after irradiation. The fundamental problem of this STTR is the “radiation Hardness” of the necessary material structures and how the material electrical and mechanical properties evolve after radiation exposure. This is the first order problem which must be addressed, both for the near and far term needs of the HEP community. The detailed work plan for this effort, is to test and quantify a material set for application to both the near and far term needs of the high energy beam lines with regard to Silicon detectors.