# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### Pixelated Charge Readout and the ArgonCube Program  
Wire-based anode planes are undoubtedly the most established technology for charge readout in single-phase LArTPCs, with decades of research and refinement behind today's designs and implementations. However, recent developments in reliable and inexpensive cryogenic electronics-such as those used for the front-end components in the SBN and DUNE programs, as previously described-have allowed for the realisation of cryogenic pixelated charge readout. Non-cryogenic implementations of this type of device have been used for almost two decades in gaseous TPCs [52], and typically feature more readout channels than wire-based readouts, as well as digitisation and multiplexing electronics situated very close to the pixels themselves, if not directly bonded to them. The underlying advantage of a pixelated charge readout is that a single anode plane is able to provide full 3D reconstruction of particle tracks in a TPC (with two coordinates provided by the positions of the triggered pixels, and the third being calculated from their relative trigger times), while not being susceptible to the ambiguities that can result from the use of wire-based anode planes. Such ambiguities can occur, for example, in high particle rate environments, where the relatively long readout windows required to fully capture all of the drifting electrons can lead to event pileup, and therefore multiple overlapping signals on the wires. However, usage of a pixelated charge readout at cryogenic temperatures requires not only that the materials and electrical connections be able to mechanically withstand the cold environment, but also that they be able to operate with very low power consumption, in order to minimise heat dissipation. In recent years, various concepts for pixelated charge readout in LArTPCs have been proposed and demonstrated, with a number of them coming through, or in collaboration with, the ArgonCube program [53]. This R&D program is broadly focused on the design and construction of the LArTPC sub-system of the DUNE near detector, with a primary goal being the implementation of a modular detector design that splits a generic large LArTPC volume into multiple smaller ones, each effectively operating as an independent TPC [53; 54]. Such a design--although more complicated in terms of construction and operation--has a number of advantages over a single monolithic detector, such as reduced purity and HV requirements (since the maximum electron drift length per TPC will be smaller), and reduced electron diffusion and scattering. In parallel with this, the development of field cages constructed from thin resistive film is aimed at reducing the amount of uninstrumented, non-active volume between the TPC modules [54]. Initial efforts at developing a pixelated charge readout for LArTPCs began in 2016 [55]. The charge-capture anode plane used in this iteration, shown in Figure 29, was a standard multi-layered PCB, with 1008 900 \(\upmu\)m vias (electrical pathways through the PCB layers) acting as the \"pixels\". The pixel-to-pixel spacing was 2.54 mm, and the pixelated area had a diameter of 100 mm, with each pixel directly coupled to a cryogenic preamplifier. The ASICs associated with these preamplifiers were the same as those used in the MicroBooNE and LArIAT detectors--i.e., they were designed for wire-based readout, and so did not have integrated digitising or multiplexing capabilities. This therefore necessitated the use of external digitisers, as well as a bespoke multiplexing algorithm that allowed the number of readout channels to be reduced from 1008 (one per pixel) to just 64 [55]. The LArTPC used for this demonstration was located at the University of Bern, and featured a cylindrical active volume measuring 10 cm in diameter and 60 cm in height (along the drift direction), operating with a drift field of 1 kV/cm [55].