Single-electron Resolution Research Articles

The DAMIC-M Low Background Chamber

The DArk Matter In CCDs at Modane (DAMIC-M) experiment is designed to search for light dark matter (m χ < 10 GeV/c2) at the Laboratoire Souterrain de Modane (LSM) in France. DAMIC-M will use skipper charge-coupled devices (CCDs) as a kg-scale active detector target. Its single-electron resolution will enable eV-scale energy thresholds and thus world-leading sensitivity to a range of hidden sector dark matter candidates. A DAMIC-M prototype, the Low Background Chamber (LBC), has been taking data at LSM since 2022. The LBC provides a low-background environment, which has been used to characterize skipper CCDs, study dark current, and measure radiopurity of materials planned for DAMIC-M. It also allows testing of various subsystems like readout electronics, data acquisition software, and slow control. This paper describes the technical design and performance of the LBC.

The DAMIC-M experiment: Status and first results

The DAMIC-M (DArk Matter In CCDs at Modane) experiment employs thick, fully depleted silicon charged-coupled devices (CCDs) to search for dark matter particles with a target exposure of 1 kg-year. A novel skipper readout implemented in the CCDs provides single electron resolution through multiple non-destructive measurements of the individual pixel charge, pushing the detection threshold to the eV-scale. DAMIC-M will advance by several orders of magnitude the exploration of the dark matter particle hypothesis, in particular of candidates pertaining to the so-called “hidden sector.” A prototype, the Low Background Chamber (LBC), with 20g of low background Skipper CCDs, has been recently installed at Laboratoire Souterrain de Modane and is currently taking data. We will report the status of the DAMIC-M experiment and first results obtained with LBC commissioning data.

Measurement of low-energy Compton and neutron scattering in Si CCDs for dark matter searches

For optimal sensitivity to low-mass dark matter candidates experiments like DAMIC-M employ skipper charged-coupled devices (CCDs) with detection threshold of just a few ionization charges. Ionization signals from small-angle Compton scatters of environmental \gammaγ-rays, an important component of the background in dark matter searches, must thus be characterized down to OO(10 eV) energy. Using a ^{241}241Am \gammaγ-ray source, we report a precise measurement of scattering on Si atomic shell electrons in a skipper CCD with single-electron resolution. Notable differences are observed between data and theoretical expectations in the L-shell energy region (&lt;150 eV). We also present preliminary data from a skipper CCD exposed to low-energy neutrons (&lt;24 keV) from a ^{124}124Sb^99Be photoneutron source, demonstrating a measurement of the nuclear recoil ionization efficiency in Si down to few ionization charges.

Room-temperature several-hundred-of-megahertz charge sensing with single-electron resolution using a silicon transistor

We demonstrate charge detection with single-electron resolution at high readout frequency using a silicon field-effect transistor (FET) integrated with double resonant circuits. A FET, whose channel of 10-nm width enables a single electron to be detected at room temperature, is connected to resonant circuits composed of coupled inductors and capacitors, and these double resonant circuits provide two resonance frequencies. When the FET is driven by a carrier signal at the lower resonance frequency, a small signal applied to the FET's gate modulates the resonance condition, resulting in a reflected signal appearing near the higher resonance frequency. Such operation utilizing the double resonant circuits enables charge detection with a single-electron resolution of 3 × 10−3 e/Hz0.5 and a readout frequency of 200 MHz at room temperature. In addition, a variable capacitor used in the double resonant circuits allows charge-sensing characteristics to be controlled in situ.

Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection

Experiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of $\mathcal{O}(1\,\mathrm{eV})$. In this regime, ionization signals from small-angle Compton scatters of environmental $\gamma$-rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23$\,$eV. A skipper charge-coupled device (CCD) with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a $^{241}$Am $\gamma$-ray source over several months. Features associated with the silicon K, L$_{1}$, and L$_{2,3}$-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100$\,$eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5$\,$keV. The data are in better agreement with $ab$ $initio$ calculations originally developed for X-ray absorption spectroscopy.

Using scientific-grade CCDs for the direct detection of dark matter with the DAMIC-M experiment

The DAMIC-M [1] project is devoted to the exploration of the hidden sector and the search for light dark matter particles using Charge-Coupled Devices (CCDs). It follows the DAMIC at SNOLAB [2] experiment which pioneered the detection of new particles through their interaction with the nucleus or the electrons of the bulk silicon of fully depleted CCDs. A kilogram-sized target mass will be installed at the Modane underground laboratory (LSM, France) which offers an excellent low background environment for rare-event search. DAMIC-M detectors demonstrate several technological advancements including the implementation of the skipper technique, and custom front-end control and read-out electronics. Skipper CCDs can perform multiple non-destructive measurements of the pixel charge which can lead to a read-out noise of a fraction of an electron. With a 15 μm × 15 μm pixel area, 675 μm thickness and the ability of 3D reconstruction using the diffusion of the particle track, the spatial resolution of our CCDs allows for the follow-up of radioactive chains, a powerful tool to discriminate genuine particle interaction from in situ radioactive decays. Together with an extremely careful fabrication procedure that controls the contaminant and the generation of bulk radioactive contamination by cosmic ray spallation, the single electron resolution will guarantee a detection energy threshold of only a few eVs, pushing the sensitivity of DAMIC-M by at least one order of magnitude better than previous experiments. I will present the current status of DAMIC-M describing our technological challenges and the solutions we have adopted. I will introduce our method to measure and mitigate the bulk radioactive contamination and discuss the ongoing assembly of a prototype detector, the Low Background Chamber (LBC), aiming at validating our design options.

DePFET—Recent Developments and Future Prospects

The DePFET is a sensor amplifier structure first proposed in 1987. In recent years, DeFPET based sensors have been deployed for particle tracking at Belle II experiment and been launched into space aboard the planetary science mission BepiColombo in its MIXS instrument. In the future DePFETs are proposed for the Wide Field Imager aboard the ATHENA satellite and developed for use as real-time imager for transmission electron microscopes These sensors have all been tailored to the needs of the respective application, providing high frame rates and accurate position resolution for tracking, Fano-limited energy resolution and position resolution matched to telescopes for X-ray spectroscopy or high frame rates and maximized dynamic range for applications on TEMs. In addition to this, several DePFET based concepts, implementing additional functionality on pixel level have been tested in recent years. Among these are the tailoring of the internal gates shape to implement a non-linear signal response and provide a larger dynamic range or a drastic increase of the DePFETs amplification. Furthermore, super pixels providing capabilities to reach sub electron noise and single electron resolution through repetitive readout, a fast electronic shutter at pixel level and the realization of multiple storage regions within one pixel have been tested. It was further demonstrated, that combinations of these features can also be realized. Over all, it is noted that advances in DePFET technology will provide sensors that are optimally tailored to the need of a specific application.

Skipper Charge-Coupled Device for Low-Energy-Threshold Particle Experiments above Ground

We present experimental results using a single-electron resolution skipper CCD running above ground level to demonstrate the potential of this technology for its use in reactor neutrino observations and other low-energy particle-interaction experiments. Operating conditions and event-selection criteria are provided to decouple most of the background rate at low energies. The majority of this background comes from interactions in the inactive silicon surrounding the active detector volume that ends up in the readout register of the sensor. Our final results are compared with other low-threshold technologies showing a good control of the background for low ionization energies down to five electron-hole pairs. This demonstrates that the skipper CCD proves to be among the best options to measure low-energy and weakly interacting particles at ground level.

Large mass single electron resolution detector for dark matter and neutrino elastic interaction searches

Large mass single electron resolution solid state detectors are desirable to search for low mass dark matter candidates and to measure coherent elastic neutrino nucleus scattering (CEνNS). Here, we present results from a novel 100 g phonon-mediated Si detector with a new interface architecture. This detector gives a baseline resolution of ∼1e−∕h+ pair and a leakage current on the order of 10−16 A. This was achieved by removing the direct electrical contact between the Si crystal and the metallic electrode, and by increasing the phonon absorption efficiency of the sensors. The phonon signal amplification in the detector shows a linear increase while the signal to noise ratio improves with bias voltage, up to 240 V. This feature enables the detector to operate at a low energy threshold which is beneficial for dark matter and CEνNS like searches.

Optical Detection of Single-Electron Tunneling into a Semiconductor Quantum Dot.

The maximum information of a dynamic quantum system is given by real-time detection of every quantum event, where the ultimate challenge is a stable, sensitive detector with high bandwidth. All physical information can then be drawn from a statistical analysis of the time traces. We demonstrate here an optical detection scheme based on the time-resolved resonance fluorescence on a single quantum dot. Single-electron resolution with high signal-to-noise ratio (4σ confidence) and high bandwidth of 10kHz make it possible to record the individual quantum events of the transport dynamics. Full counting statistics with factorial cumulants gives access to the nonequilibrium dynamics of spin relaxation of a singly charged dot (γ_{↑↓}=3 ms^{-1}), even in an equilibrium transport measurement.

Velocity-dependent dark matter interactions in single-electron resolution semiconductor detectors with directional sensitivity

We investigate the velocity and recoil momentum dependence of dark matter interactions with ordinary matter. In particular we focus on the single-electron resolution semiconductor detectors, which allow experimental assessment of sub-GeV dark matter masses. We find that, within a specific mass range depending on the detector material, the dark matter interactions result in a signal characterized by daily modulation. Furthermore, we find that the detailed structure of this modulation is sensitive to the velocity and momentum dependence of dark matter interactions. We identify the optimal mass range for the prevalence of these effects.

Directional Sensitivity in Light-Mass Dark Matter Searches with Single-Electron-Resolution Ionization Detectors.

We propose a method using solid state detectors with directional sensitivity to dark matter interactions to detect low-mass weakly interacting massive particles (WIMPs) originating from galactic sources. In spite of a large body of literature for high-mass WIMP detectors with directional sensitivity, no available technique exists to cover WIMPs in the mass range <1 GeV/c^{2}. We argue that single-electron-resolution semiconductor detectors allow for directional sensitivity once properly calibrated. We examine the commonly used semiconductor material response to these low-mass WIMP interactions.

MCP performance improvement using alumina thin film

The performance improvement using alumina thin film on a dual microchannel plate (MCP) detector for single electron counting was investigated. The alumina thin film was coated on all surfaces of the MCPs by atomic layer deposition method. It was found that the gain, the single electron resolution and the peak-to-valley ratio of the dual MCP detector were significantly enhanced by coating the alumina thin film. The optimum operating conditions of the new dual MCP detector have been studied.

Toward single electron resolution phonon mediated ionization detectors

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ∼14eVee. CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5GeV/c2 but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a×2 Luke phonon gain, world best RMS resolution of sigma ∼7eVee for 0.25kg (d=75mm, h=1cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25mm) will reach a resolution of ∼2.8eVee. In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

Quantum state readout of individual quantum dots by electrostatic force detection

Electric charge detection by atomic force microscopy (AFM) with single-electron resolution (e-EFM) is a promising way to investigate the electronic level structure of individual quantum dots (QDs). The oscillating AFM tip modulates the energy of the QDs, causing single electrons to tunnel between QDs and an electrode. The resulting oscillating electrostatic force changes the resonant frequency and damping of the AFM cantilever, enabling electrometry with a single-electron sensitivity. Quantitative electronic level spectroscopy is possible by sweeping the bias voltage. Charge stability diagram can be obtained by scanning the AFM tip around the QD. e-EFM technique enables to investigate individual colloidal nanoparticles and self-assembled QDs without nanoscale electrodes. e-EFM is a quantum electromechanical system where the back-action of a tunneling electron is detected by AFM; it can also be considered as a mechanical analog of admittance spectroscopy with a radio frequency resonator, which is emerging as a promising tool for quantum state readout for quantum computing. In combination with the topography imaging capability of the AFM, e-EFM is a powerful tool for investigating new nanoscale material systems which can be used as quantum bits.

Investigation of the Program Operation of NAND Flash Cells With a Single-Electron Resolution

This paper exploits the possibility of monitoring the floating-gate (FG) charge of state-of-the-art NAND Flash arrays with a single-electron resolution to investigate in detail the program operation and some previously inaccessible technological parameters. In particular, the analysis leads to the assessment of the statistical distribution of the FG to control-gate capacitance and of the leakage current from the FG through the intergate dielectric during the programming pulses. Results highlight that resolving the FG charge at the single-electron level opens new prospects for the investigation of the operation and the parameters of NAND Flash arrays.

Wide-bandwidth charge sensitivity with a radio-frequency field-effect transistor

We demonstrate high-speed charge detection at room temperature with single-electron resolution by using a radio-frequency field-effect transistor (RF-FET). The RF-FET combines a nanometer-scale silicon FET with an impedance-matching circuit composed of an inductor and capacitor. Driving the RF-FET with a carrier signal at its resonance frequency, small signals at the transistor's gate modulate the impedance of the resonant circuit, which is monitored at high speed using the reflected signal. The RF-FET driven by high-power carrier signals enables a charge sensitivity of 2 × 10−4 e/Hz0.5 at a readout bandwidth of 20 MHz.

Single-Photon Resolution CMOS Integrating Image Sensors

A CMOS image sensor – realized in a commercially available 0.18μm CIS technology – for near “single-photon detection” applications is presented. The pixel array features 1.2e- readout noise and 2.5e- overall noise comprising dark current shot noise effects at 60 frames per second (16μs row-time). The 11μm x 11μm pixel (fill factor of 63%) provides a pixel conversion gain of 50μV/e-. High-dynamic range of over 150dB is achieved.Further research on noise in charge detector circuits has resulted in the invention of a novel ultra-low-noise pixel featuring in-pixel amplification enabling single-electron resolution imaging. A typical sense node referred readout noise of 0.9e- and an overall sense node referred noise floor of 1.5e- are measured at a pixel conversion gain of 300μV/e-.

Infrared detection with silicon nano-field-effect transistors

The authors fabricated nanoscale silicon metal-oxide-semiconductor field-effect transistors (MOSFETs) to detect an infrared (IR) signal at room temperature. The IR signal excites conduction-band electrons in an undoped channel of a MOSFET and some of them are injected through an energy barrier into a storage node (SN) electrically formed by the MOSFET. Small signals, originating from electrons, stored in the SN are detected by an electrometer with a single-electron resolution. Additionally, the MOSFET controls the number and energy of electrons injected into the SN. This enables electrical control of the sensitivity and cutoff wavelengths of IR signals, suggesting the possibility of highly functional IR sensors.

Submicron sensors of local electric field with single-electron resolution at room temperature

We describe probes of a local electric field, which are capable of detecting an electric charge as small as the charge of one electron e, operational under ambient conditions and having a spatial resolution down to 100nm. The submicron-sized probes were made from a high-density high-mobility two-dimensional electron gas, which is sensitive to the presence of electric charges near its surface. We demonstrate the possibility of using such microprobes for life-science applications by measuring an electric response of individual yeast cells to abrupt changes in their environment.