# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### Pixelated Charge Readout and the ArgonCube Program
Analysis of cosmic muonevents captured by the detector showed that a pixelated charge-capture anode plane is indeed a viable method of reading out a LArTPC, with good a signal-to-noise ratio and precise 3D reconstruction of particle tracks. However, certain limitations were observed, largely related to the aforementioned use of wire-based readout electronics [55]. This made it clear that any further research into pixelated charge readouts would have to include development of dedicated electronics. Bespoke per-pixel electronics were introduced by the LArPix readout system in 2018 [56]. In contrast to the vias used by the first iteration, the pixels used by LArPix were gold-plated copper pads with 3 mm spacing, etched onto the surface of a standard dual-layer \"pixel PCB\". Two pixel PCBs were used during the development and operation of LArPix-one containing 832 pixels and an active area 10 cm in diameter (shown in Figure 30), and the other with 512 pixels covering a 4.8 \(\times\) 9.6 cm area. Both used pixels of varying size and shape, for the purposes of evaluating the optimal pixel characteristics. The connected ASICs were located on a separate \"data PCB\" above the pixel PCB, with a shielding layer in between to reduce cross-talk between the PCBs, and with 32 pixels wire-bonded to each ASIC [56]. The ASICs and PCBs were all manufactured using standard commercial fabrication methods. Central to each pixel's individual readout was a charge-sensitive amplifier connected to a discriminator and digitiser. As the charge built on a pixel, the amplifier's output signal would also increase, and if it subsequently passed a threshold set by the discriminator, it would be passed to the digitiser, after which the amplifier would be reset. This system is therefore the basis of a \"self-triggering\" pixel readout. (A full description of the LArPix ASICs and associated electronics is given in [56].) A multiplexing scheme that allowed all of the ASICs to be controlled and read out using a single input and output line respectively was also designed and evaluated. The LArPix pixelated charge readouts were tested on two detectors, both at the University of Bern: the 832-pixel iteration was used on a 10 cm diameter, 10 cm tall LArTPC, and the 512-pixel version on the same 10 cm diameter, 60 cm tall setup previously used by the 2016 iteration. Analysis of the collected cosmic muon events from both versions demonstrated the excellent capability of the readouts, showing clean and unambiguous identification of particle tracks with no requirement for noise filtering or external signal amplification, as seen in Figure 31. Testing also demonstrated that the readout electronics were stable and reliable over periods of up to a week of continuous operation, and exhibited  
Figure 29: The first pixelated charge-capture anode plane developed for the ArgonCube program. It consists of a standard multi-layered PCB, with 1008 900 \(\upmu\)m vias with 2.54 mm spacing acting as pixels. The vias are grouped into 28 6 \(\times\) 6 pixel “regions of interest” for the purposes of multiplexed readout, and the pixelated area is 100 mm in diameter. Taken from [55]. a very low noise rate (\(<\)500 electron-equivalent total charge across the entire system) and power consumption (\(<\)100 uW per pixel) [56]. Some performance limitations were identified-such as the impact of signal shaping on the precise time of threshold crossing in the discriminator, and the loss of integrated charge during the dead-time between threshold crossing and the amplifier resetting-and further development of the ASIC and associated readout electronics is aimed at addressing such issues. Development and implementation of the ArgonCube modular detector design continues alongside the LArPix program. A demonstrator, which uses a 2 \(\times\) 2 array of TPCs  
Figure 31: **(Left)** A cosmic muon track as seen by the 832-pixel LArPix readout. **(Right)** An electromagnetic shower as seen by the 512-pixel readout.