Advanced fabrication process for particle absorbers of highly pure electroplated gold for microcalorimeter applications

TL;DR

This paper introduces a novel microfabrication process for creating high-purity, free-standing gold particle absorbers with optimized electroplating, enhancing the performance of magnetic microcalorimeters in various scientific applications.

Contribution

It presents a new fabrication method for high-purity gold absorbers with independent electroplating layers, enabling advanced detector designs for microcalorimeter applications.

Findings

High residual resistivity ratio (>40) of gold films.

Enables embedding radioactive sources within absorbers.

Supports variable quantum efficiency and energy resolution.

Abstract

Magnetic microcalorimeters (MMCs) have become a key technology for applications requiring outstanding energy resolution, fast signal rise time and excellent linearity. MMCs measure the temperature rise upon absorption of a single particle within a particle absorber by using a paramagnetic temperature sensor that is thermally coupled to the absorber. The design and fabrication of the particle absorber is key for excellent detector performance. Here, we present a microfabrication process for free-standing particle absorbers made of two stacked and independently electroplated high-purity Au layers. This enables, for example, embedding of radioactive sources within the absorber for realizing a $4\pi$ detection geometry in radionuclide metrology or preparing detector arrays with variable quantum efficiency and energy resolution as requested for future applications in high energy physics. Due to careful optimization of photoresist processing and electroplating parameters, the Au films are of very high purity and very high residual resistivity ratio values above 40, allowing for fast internal absorber thermalization.