This study introduces an implantable piezoelectric ultrasound stimulator (ImpULS) for precise and localized deep brain stimulation. ImpULS is a flexible, biocompatible piezoelectric micromachined ultrasound transducer (pMUT) that generates ultrasonic pressure up to 100 kPa to modulate neuronal activity. The device uses potassium sodium niobate (KNN) as the piezoelectric material, which is lead-free and offers high piezoelectric efficiency and durability. ImpULS is designed to be implanted in the brain, where it can stimulate neurons in specific regions, such as the hippocampus and substantia nigra pars compacta (SNc), with high spatial resolution and minimal thermal effects. ImpULS was tested in various conditions, including in vitro and in vivo experiments. In vitro, it successfully stimulated neurons in a hippocampal slice and activated hippocampal cells in anesthetized mice, inducing expression of the activity-dependent gene c-Fos. In vivo, it stimulated dopaminergic neurons in the SNc, eliciting time-locked modulation of striatal dopamine release. The device demonstrated long-term stability, with minimal degradation after 7 days in a phosphate-buffered saline solution at 75°C. It also showed low temperature rise during operation, well below the threshold for neuromodulation. ImpULS offers several advantages over existing neurostimulation methods, including no exposed electrochemical area, which reduces biofouling and corrosion, and a smaller size compared to traditional deep brain stimulation (DBS) devices. It can be implanted with minimal tissue damage and provides precise, localized stimulation without off-target effects. The device's ability to modulate neural activity through ultrasound, without genetic modification, makes it a promising tool for both basic neuroscience research and potential therapeutic applications. The study highlights the potential of ultrasound-based neurostimulation for precise and safe modulation of neural activity in the deep brain, with implications for the treatment of neurological disorders such as Parkinson's disease, epilepsy, and depression. Future research could focus on improving the device's performance, expanding its application to different brain regions, and integrating it with other technologies for more advanced neurostimulation.This study introduces an implantable piezoelectric ultrasound stimulator (ImpULS) for precise and localized deep brain stimulation. ImpULS is a flexible, biocompatible piezoelectric micromachined ultrasound transducer (pMUT) that generates ultrasonic pressure up to 100 kPa to modulate neuronal activity. The device uses potassium sodium niobate (KNN) as the piezoelectric material, which is lead-free and offers high piezoelectric efficiency and durability. ImpULS is designed to be implanted in the brain, where it can stimulate neurons in specific regions, such as the hippocampus and substantia nigra pars compacta (SNc), with high spatial resolution and minimal thermal effects. ImpULS was tested in various conditions, including in vitro and in vivo experiments. In vitro, it successfully stimulated neurons in a hippocampal slice and activated hippocampal cells in anesthetized mice, inducing expression of the activity-dependent gene c-Fos. In vivo, it stimulated dopaminergic neurons in the SNc, eliciting time-locked modulation of striatal dopamine release. The device demonstrated long-term stability, with minimal degradation after 7 days in a phosphate-buffered saline solution at 75°C. It also showed low temperature rise during operation, well below the threshold for neuromodulation. ImpULS offers several advantages over existing neurostimulation methods, including no exposed electrochemical area, which reduces biofouling and corrosion, and a smaller size compared to traditional deep brain stimulation (DBS) devices. It can be implanted with minimal tissue damage and provides precise, localized stimulation without off-target effects. The device's ability to modulate neural activity through ultrasound, without genetic modification, makes it a promising tool for both basic neuroscience research and potential therapeutic applications. The study highlights the potential of ultrasound-based neurostimulation for precise and safe modulation of neural activity in the deep brain, with implications for the treatment of neurological disorders such as Parkinson's disease, epilepsy, and depression. Future research could focus on improving the device's performance, expanding its application to different brain regions, and integrating it with other technologies for more advanced neurostimulation.