This paper introduces an implantable piezoelectric ultrasound stimulator (ImPULS) designed to modulate neuronal activity in deep brain regions. ImPULS is a flexible, encapsulated, and biocompatible device that generates ultrasonic focal pressure of 100 kPa to activate neurons. The device uses potassium sodium niobate [(K,Na)NbO3] as the active piezoelectric material, which lacks electrochemically active elements, ensuring long-term stability. Key findings include: 1. **Design and Fabrication**: ImPULS is a micron-scale, flexible piezoelectric micromachined ultrasound transducer (pMUT) with a thickness of 30 μm and an active piezo element diameter of 100 μm. It is fabricated using a transfer printing process, integrating biocompatible materials and a polymer substrate. 2. **Performance Characterization**: The device operates at a resonant frequency of 500 kHz, generating a maximum pressure of 100 kPa at a distance of 15 μm. It demonstrates consistent resonant behavior and minimal heating (<1°C) in different mediums. 3. **In Vivo Stimulation**: ImPULS successfully stimulated neurons in a mouse hippocampal slice ex vivo and activated cells in the hippocampus of an anesthetized mouse, inducing c-Fos expression. It also modulated dopaminergic neurons in the substantia nigra pars compacta (SNc), leading to time-locked modulation of nigrostriatal dopamine release. 4. **Durability and Biocompatibility**: ImPULS remains functional after 7 days in an accelerated aging test and shows minimal damage. It is biocompatible, as confirmed by cell viability tests and immunohistochemical staining. 5. **Discussion**: ImPULS offers advantages over electrode-based deep brain stimulation, such as avoiding biofouling and corrosion, and providing precise and potent stimulation. It has potential for both therapeutic applications and neuroscience research, particularly in treating neurological disorders and exploring deep brain functions. This work presents a versatile and non-genetic platform for localized neurostimulation, highlighting its potential as a tool for advanced neural interfaces.This paper introduces an implantable piezoelectric ultrasound stimulator (ImPULS) designed to modulate neuronal activity in deep brain regions. ImPULS is a flexible, encapsulated, and biocompatible device that generates ultrasonic focal pressure of 100 kPa to activate neurons. The device uses potassium sodium niobate [(K,Na)NbO3] as the active piezoelectric material, which lacks electrochemically active elements, ensuring long-term stability. Key findings include: 1. **Design and Fabrication**: ImPULS is a micron-scale, flexible piezoelectric micromachined ultrasound transducer (pMUT) with a thickness of 30 μm and an active piezo element diameter of 100 μm. It is fabricated using a transfer printing process, integrating biocompatible materials and a polymer substrate. 2. **Performance Characterization**: The device operates at a resonant frequency of 500 kHz, generating a maximum pressure of 100 kPa at a distance of 15 μm. It demonstrates consistent resonant behavior and minimal heating (<1°C) in different mediums. 3. **In Vivo Stimulation**: ImPULS successfully stimulated neurons in a mouse hippocampal slice ex vivo and activated cells in the hippocampus of an anesthetized mouse, inducing c-Fos expression. It also modulated dopaminergic neurons in the substantia nigra pars compacta (SNc), leading to time-locked modulation of nigrostriatal dopamine release. 4. **Durability and Biocompatibility**: ImPULS remains functional after 7 days in an accelerated aging test and shows minimal damage. It is biocompatible, as confirmed by cell viability tests and immunohistochemical staining. 5. **Discussion**: ImPULS offers advantages over electrode-based deep brain stimulation, such as avoiding biofouling and corrosion, and providing precise and potent stimulation. It has potential for both therapeutic applications and neuroscience research, particularly in treating neurological disorders and exploring deep brain functions. This work presents a versatile and non-genetic platform for localized neurostimulation, highlighting its potential as a tool for advanced neural interfaces.