Hybrid CMOS-OxRAM Image Sensor for Overexposure Control

Abstract

This paper presents a first of its kind unique application of OxRAM devices in CMOS image sensor pixels. Our proposed hybrid CMOS-OxRAM pixel circuit exploits the non-linear capacitive and resistive properties of OxRAM device to control image overexposure autonomously. HfOx based OxRAM device is used as a programmable capacitive load in a conventional 4T-APS (active pixel sensor) circuit. Our solution exploiting HfOx based OxRAM devices, improves the dynamic range of individual pixels by a factor of ∼ 2.45 (or 7.8 dB), and capacitance density by a factor of ∼5 at 180 nm node.

Exploiting OxRAM Resistive Switching for Dynamic Range Improvement of CMOS Image Sensors

“…The effect of OxRAM's intrinsic capacitance (C P OX ) on the proposed pixel can be deduced from equation (4). In our previous work [13], we have presented a detailed analysis of OXRAM capacitance calculation and its exploitation for the pixel performance improvement in bright light stimuli. However for the resistive use case described in this paper (with dim-light stimuli), C P OX actually degrades the improvement factor of the pixel DR. Higher value of C P OX leads to a low charge to voltage conversion gain or low pixel sensitivity.…”

“…In particular, we show in [13] how non-linear CV of HfOx based OxRAM, can be used to enhance the DR of a 4T CMOS pixel by a factor of 2.45 X. The OxRAM in our previous approach [13] is essentially used as a high density non-linear MIMCAP, always programmed in a strong HRS state with no resistive switching event taking place during exposure or pixel operation.…”

“…In recent work [13], we showed that capacitive properties of OxRAM devices (Metal oxide based resistive nonvolatile memory) [14], [15] can be exploited for pixel DR improvement in bright-light conditions. In particular, we show in [13] how non-linear CV of HfOx based OxRAM, can be used to enhance the DR of a 4T CMOS pixel by a factor of 2.45 X.…”

“…In recent work [13], we showed that capacitive properties of OxRAM devices (Metal oxide based resistive nonvolatile memory) [14], [15] can be exploited for pixel DR improvement in bright-light conditions. In particular, we show in [13] how non-linear CV of HfOx based OxRAM, can be used to enhance the DR of a 4T CMOS pixel by a factor of 2.45 X. The OxRAM in our previous approach [13] is essentially used as a high density non-linear MIMCAP, always programmed in a strong HRS state with no resistive switching event taking place during exposure or pixel operation.…”

Exploiting analogue OxRAM conductance modulation for contrast enhancement application

“…High integration density, low power, low fabrication cost, CMOS compatibility [1] and full back-end integration, make OxRAM a suitable candidate for many applications. Recent studies have also proposed different OxRAM devices for image-sensing and imageprocessing related application use-cases such as event-detection [4], feature extraction [5], sparse encoding [6], recognition [7], compression [8], overexposure/underexposure control [9,10], dynamic range improvement [11] and real-time background tracking [12]. At the same time, unlike conventional vision systems, biological vision systems are known to perform more efficiently [13][14][15] on real-world vision tasks.…”