## 1 Introduction  
Recent years have seen significant advancements in micro-pattern gaseous detectors (MPGDs). Gaseous electron multipliers (GEMs) [1] and thick gaseous electron multipliers (THGEMs) (also know as large electron multipliers (LEMs)) [2] are some of the most recent developments within the field of MPGDs and have proved important for their simplicity and effectiveness. GEMs and THGEMs both have similar basic arrangements: an insulating substrate, sandwiched between two electrically conductive electrodes, with holes perforating through all three layers. Compared to GEMs, THGEMs typically have an order of magnitude increased thickness. Traditionally, THGEMs are manufactured from an epoxy laminate/FR4 substrate and have copper plated electrodes. Sub-millimetre through holes are mechanically drilled through the device to form field amplification regions. A dielectric rim may be etched around each hole. It has been reported that dielectric rims reduce the probability of discharges, ultimately resulting in ten-fold higher gain compared to designs without rims [3]. The robustness and simplicity of THGEMs, both in terms of their use and manufacturing, have resulted in their adoption in a wide variety of applications. This paper will concentrate on their use in dual-phase and gaseous time project chambers (TPCs). Typically, TPCs can either be filled completely with a scintillating gas or, in the dual-phase case, filled with both the liquid and gaseous state of a single scintillator (typically argon or xenon). When an ionising particle passes through the TPC volume, both scintillation light and free electrons are produced. By means of an applied electric field, the free electronsare drifted to the surface of the TPC, which is typically covered by devices capable of detecting these electrons. By detecting both the scintillation light and the ionised electron signal, event reconstruction within the TPC is possible. In the case of gaseous TPCs, both initial scintillation/ionisation and detection are performed in the gas. In dual-phase TPCs, initial scintillation/ionisation occurs in the liquid, affording the benefit of increased target density. The ionised signal is drifted and extracted into the gaseous phase for detection. The benefit of extraction into a gaseous phase is retaining the ability to amplify the ionised signal using MPGDs, which typically offer favourable performance when operating in gas compared to liquid. The effectiveness of THGEMs has resulted in their widespread use within the contemporary TPC field, and much development has been made including the production of liquid hole multipliers and FAT GEMs [4]. TPCs are now integral within the neutrino and dark matter sectors, with the proposed kiloton scale DUNE modules [5; 6; 7; 8; 9; 10; 11], CYGNO [12], DarkSide-20k [13], ArDM [14] and LZ [15]. Despite the many attractive features of THGEMs, there are limitations in terms of their design and manufacture. Conventionally, THGEMs may be manufactured using standard printed circuit board (PCB) techniques. This typically results in THGEMs produced from epoxy laminate/FR4 substrates. Epoxy laminate/FR4 typically contains radioactive contaminants, precluding use within the dark matter community. Additionally, epoxy laminate/FR4 is a porous material, hence contamination, moisture absorption and out-gassing issues may occur. Large area THGEMs/LEMs typically require mechanical support within the active area to limit deformations caused by sagging under gravity. Variations in epoxy laminate/FR4 thickness across the substrate may also result in variations in field (and therefore gain) across the THGEM. The use of substrates with higher stiffness and stricter thickness tolerances may alleviate both of these issues. Repeated sparking and discharging of THGEMs during operation may eventually lead to carbonisation of the epoxy laminate/FR4 substrates. Carbonisation forms a conductive pathway between electrodes, leading to degraded THGEM performance over time, potentially resulting in device failure.