The detection of low-level light is a key technology in various experimental scientific studies.As a photon detector,the silicon photomultiplier(SiPM) has gradually become an alternative to the photomultiplier tube(PMT) in many applications in high-energy physics,astroparticle physics,and medical imaging because of its high photon detection efficiency(PDE),good resolution for single-photon detection,insensitivity to magnetic field,low operating voltage,compactness,and low cost.However,primarily because of the geometric fill factor,the PDE of most SiPMs is not very high; in particular,for those SiPMs with a high density of micro cells,the effective area is small,and the bandwidth of the light response is narrow.As a building block of the SiPM,the concept of the backside-illuminated avalanche drift detector(ADD) was first proposed by the Max Planck Institute of Germany eight years ago; the ADD is promising to have high PDE over the full energy range of optical photons,even ultraviolet light and X-ray light,and because the avalanche multiplication region is very small,the ADD is beneficial for the fabrication of large-area SiPMs.However,because of difficulties in design and fabrication,no significant progress had been made,and the concept had not yet been verified.In this paper,preliminary results in the design,fabrication,and performance of a backside-illuminated ADD are reported; the difficulties in and limitations to the backside-illuminated ADD are analyzed. The detection of low-level light is a key technology in various experimental scientific studies. As a photon detector, the silicon photomultiplier (SiPM) has gradually become an alternative to the photomultiplier tube (PMT) in many applications in high-energy physics, astroparticle physics, and medical imaging because of its high photon detection efficiency (PDE), good resolution for single-photon detection, insensitivity to magnetic field, low operating voltage, compactness, and low cost. Nearly because of the geometric fill factor, the PDE of most SiPMs is not very high; in particular, for those SiPMs with a high density of micro cells, the effective area is small, and the bandwidth of the light response is narrow. As a building block of the SiPM, the concept of the backside-illuminated avalanche drift detector (ADD) was first proposed by the Max Planck Institute of Germany eight years ago; the ADD is promising to have high PDE over the full energy range of optical photons, even ultraviolet li ght and X-ray light, and because the avalanche multiplication region is very small, the ADD is beneficial for the fabrication of large-area SiPMs.However, because of difficulties in design and fabrication, no significant progress had been made, and the concept had not yet been verified.In this paper, preliminary results in the design, fabrication, and performance of a backside-illuminated ADD are reported; the difficulties in and limitations to the backside-illuminated ADD are analyzed.