Wearable Systems with Stacked Photodetector Assemblies

A wearable system for use by a user, comprising:

• a stacked photodetector assembly comprising:
• a first wafer including
• a single photon avalanche diode (SPAD), and
• a fast gating circuit electrically coupled to the SPAD and configured to arm and disarm the SPAD,
• the first wafer having a thickness T1 configured to minimize absorption by the first wafer of photons included in light incident upon the first wafer while the SPAD is in a disarmed state;
• and
• a second wafer having a thickness T2 bonded to the first wafer in a stacked configuration and configured to provide structural support for the first wafer, the second wafer not including circuitry configured to control the SPAD.

A wearable system for use by a user, comprising:

• a stacked photodetector assembly comprising:
• a single photon avalanche diode (SPAD);
• a fast gating circuit electrically coupled to the SPAD and configured to arm and disarm the SPAD;
• a first wafer including the SPAD and the fast gating circuit, the first wafer having a thickness T1 configured to minimize absorption of photons included in light incident upon the first wafer while the SPAD is in a disarmed state;
• and
• a handle wafer having a thickness T2 bonded to the first wafer in a stacked configuration.

A wearable system for use by a user, comprising:

• a stacked photodetector assembly comprising:
• a single photon avalanche diode (SPAD);
• a fast gating circuit electrically coupled to the SPAD and configured to arm and disarm the SPAD;
• a first wafer including the SPAD, the first wafer having a thickness T1 configured to minimize absorption of photons included in light incident upon the first wafer while the SPAD is in a disarmed state;
• and
• a second wafer having a thickness T2 bonded to the first wafer in a stacked configuration;
• wherein the fast gating circuit includes a capacitor configured to:
• be charged, while the SPAD is in the disarmed state, with a bias voltage by a voltage source, and
• supply, while the SPAD is in an armed state, the bias voltage to an output node of the SPAD such that a voltage across the SPAD is greater than a breakdown voltage of the SPAD.